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

Despite the high specific capacity of P′2-Na x MnO 2 (NMO), its practical application is severely hindered by rapid capacity decay caused by drastic structural evolution. Herein, a P′2-[Na 0.57 K x Zn 0.10- x ]Mn 0.90 Ti 0.10 O 2 (NK x ZMTO) cathode featuring K + and Zn 2+ as pillar cations is developed to mitigate O 2– -O 2– electrostatic repulsion and suppress detrimental phase transition. Physicochemical characterization and theoretical calculations reveal that K + and Zn 2+ co-occupy the Na e site, acting as inert pillars in the Na layers. While NMO undergoes an abrupt and irreversible OP4-P′2-P″2 triphase transition, NK 0.02 ZMTO 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 Zn 2+: K + enlarges the Na layer spacing owing to its large ionic radius, while Zn 2+ reduces the electron density on O 2– through its high positive charge, thereby simultaneously mitigating O 2– -O 2– electrostatic repulsion in accordance with Coulomb’s law. Benefiting from this structural stabilization, NK 0.02 ZMTO 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.