Band‐Center Engineering: Soft Sulfur Redox Chemistry Eliminates Oxygen‐Induced Instability

ABSTRACT Sodium‐ion batteries have emerged as a cost‐effective solution for grid‐scale energy storage, intensifying the search for high‐performance cathode materials. P2‐type Na x MnO 2 , despite its high theoretical capacity and low cost, suffers from structural degradation at high voltages. Herein, we directly link this failure to irreversible lattice oxygen release and phase collapse triggered at high voltages. To overcome this issue, we pioneer a band‐center engineering strategy through sulfur anion substitution in the oxygen lattice. This approach effectively downshifts the O 2p‐band center while introducing a higher‐lying S 3p‐band, thereby fundamentally altering the anionic redox landscape. This anionic doping not only suppresses irreversible oxygen oxidation but also enables reversible sulfur redox activity. Crucially, the incorporated sulfur enhances the structural integrity by inhibiting detrimental manganese migration, thereby preserving particle morphology without cracking after extensive cycling. The optimized S‐doped P2‐Na x MnO 2‐y S y cathode delivers a remarkable long‐term cycling performance, retaining 97% of its capacity after 1000 cycles at 0.5 A g −1 , starkly outperforming the 18% retention of its pristine counterpart. This work provides atomic‐level insights into how anionic regulation stabilizes the cathode structure, establishing a practical pathway toward durable manganese‐based oxide cathodes.