Mitigating Oxygen Electrostatic Repulsion in P′2 Mn-Based Layered Oxide Cathodes via K+/Zn2+ Dual Pillaring for Highly Stable Sodium-Ion Batteries

Despite the high specific capacity of P′2-NaxMnO2 (NMO), its practical application is severely hindered by rapid capacity decay caused by drastic structural evolution. Herein, a P′2-[Na0.57KxZn0.10-x]Mn0.90Ti0.10O2 (NKxZMTO) cathode featuring K+ and Zn2+ as pillar cations is developed to mitigate O2–-O2– electrostatic repulsion and suppress detrimental phase transition. Physicochemical characterization and theoretical calculations reveal that K+ and Zn2+ co-occupy the Nae site, acting as inert pillars in the Na layers. While NMO undergoes an abrupt and irreversible OP4-P′2-P″2 triphase transition, NK0.02ZMTO maintains a high fraction of P layers within the OP4 phase and exhibits a mild and reversible P′2-OP4 biphase transition. This stabilized interlayer evolution arises from the combined effects of K+ and Zn2+: K+ enlarges the Na layer spacing owing to its large ionic radius, while Zn2+ reduces the electron density on O2– through its high positive charge, thereby simultaneously mitigating O2–-O2– electrostatic repulsion in accordance with Coulomb’s law. Benefiting from this structural stabilization, NK0.02ZMTO delivers superior cyclability (99.2% capacity retention after 150 cycles at 100 mA g–1) and a high specific capacity of 180 mAh g–1 at 10 mA g–1. This work provides an innovative strategy for designing highly stable cathode materials.