Nonequilibrium Restoration of Air-Degraded Layered Oxide Cathodes via Transient Thermal Processing for Sodium-Ion Batteries

Layered sodium transition-metal oxides are promising cathodes for sodium-ion batteries (SIBs) but suffer from severe air-induced degradation caused by surface contaminants. Herein, a nonequilibrium processing strategy for restoring air-degraded layered NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) cathodes is demonstrated. Transient thermal enables rapid surface restoration via carbonate-assisted repair of the Na-deficient layered structure while maintaining the integrity of the bulk framework. Consequently, the repaired cathode exhibits an initial Coulombic efficiency of 95.0%, significantly outperforming the 81.6% of its air-degraded counterpart, alongside a restored discharge capacity from 104.3 to 148.7 mAh g −1 . Moreover, pouch cells assembled with the repaired NFM cathode and commercial hard carbon deliver 79.2% capacity retention after 300 cycles. More encouragingly, the thermally restored NFM exhibits notably reduced air sensitivity, with only mild interface carbonation reappearing after two days of exposure. This scalable post-treatment provides an effective strategy for restoring and stabilizing air-sensitive electrode materials.