Mechanistic Insights into Oxygen Release from Layered Oxide Cathodes for Reliable Sodium‐Ion Batteries

Oxygen release from cathode materials is a serious atomistic‐scale problem causing thermal runaway of rechargeable batteries. Understanding the mechanism of oxygen release and establishing design principles for robust cathode materials are crucial for the practical implementation of sodium‐ion batteries (SIBs). Herein, it is successful, for the first time, to the elucidate mechanism of oxygen release from SIB cathode Na 2/3 Ni 1/3 Mn 2/3 O 2 by combining experimental and theoretical studies and to provide evidences for the superior stability of SIBs. Coulometric titration, X‐ray absorption spectroscopy and defect‐chemical/thermodynamic analyses reveal that the oxygen release energy of Na 2/3 Ni 1/3 Mn 2/3 O 2 is approximately 1.7 eV which is higher than those of high‐Ni lithium‐ion battery cathodes. Density functional theory calculations strongly suggest that high‐valent Ni formed by Na‐deficiency destabilizes lattice oxygen in Na 2/3 Ni 1/3 Mn 2/3 O 2 and facilitates oxygen release. The combined experimental and theoretical study presented here enables a deeper mechanistic understanding of oxygen release from cathode materials and offers valuable design insights for next‐generation batteries.