First‐Principles Investigation of Point Defects in Na‐Antiperovskite Cathodes

ABSTRACT Sodium antiperovskites have emerged as promising cathode materials for next‐generation sodium‐ion batteries owing to their structural flexibility and high sodium content. In this work, we present a comprehensive first‐principles investigation of point defects and sodium diffusion in defect containing Na‐rich antiperovskites (, where TM = 3d transition metals). The formation energies of Frenkel (Na, S, O, and transition metal) and Schottky ( and ) defect pairs are systematically evaluated under neutral charge conditions to elucidate the intrinsic defect chemistry and thermodynamic stability. Among all defect types, TM‐Frenkel and Na‐Frenkel pairs exhibit the lower formation energies, suggesting their predominance under equilibrium conditions. The energy above hull calculation (2–97 eV/atom) suggests that the Na‐Frenkel defect containing structures are metastable. The influence of Na‐Frenkel defects on sodium migration is further explored through diffusion pathway analysis using climbing image nudged elastic band method, revealing reduced activation barriers and enhanced Na mobility in the defected lattice, especially along (011) direction. Finally, interfacial thermodynamics between these Na‐antiperovskite cathodes with Na‐Frenkel defect pairs and representative solid electrolytes are examined to assess chemical compatibility and interphase stability. These results provide atomistic insight into defect‐mediated ionic transport and interfacial stability, guiding the design of high‐performance Na‐antiperovskite‐based cathodes.