First-principles modeling of structural and RedOx processes in high-voltage Mn-based cathodes for sodium-ion batteries

Sodium-ion batteries are increasingly regarded as a sustainable alternative to lithium-ion technology for large-scale energy storage, but their development remains limited by the lack of durable high-energy cathodes. Among the most promising candidates, P2–Mn-based layered oxides combine high theoretical capacity with structural versatility, yet their performance is constrained by two degradation pathways: (i) the irreversible participation of lattice oxygen in the redox process and (ii) voltage-driven solid-state phase transitions. This research article synthesizes our recent ab initio investigations aimed at disentangling the atomistic origins of these processes occurring in the high-voltage regime. We show that Mn deficiency activates oxygen redox but also promotes O2 release, whereas Fe and Ru doping strengthen TM–O covalency, enabling reversible anionic redox. In parallel, we identify cooperative Jahn–Teller distortions and Na+/vacancy reorganization as the driving forces of high-voltage phase transitions and propose simple geometric descriptors as predictive tools for structural stability. Together, these insights help to establish quantum-based design guidelines for layered sodium cathodes: reinforce TM–O covalency, suppress oxygen evolution, and mitigate phase instabilities. By combining first-principles modeling with targeted compositional design, we pave the way toward the accelerated discovery of sustainable, cobalt-free, and high-energy cathodes for next-generation sodium-ion batteries.