Na-Layer K+ Pillaring with CeO2 Coating Enables High-Rate and Air-Stable P2-Type NaMn-Layered Oxide Cathodes

Abstract

P2-type NaxMnO2 cathodes offer high capacity and elemental abundance, yet their practical application is limited by the Jahn–Teller distortion of Mn3+ and irreversible phase transitions that drive structural degradation, capacity fading, and air sensitivity. Prevailing strategies rely predominantly on element substitution at transition-metal sites, whether via single or dual doping, or in combination with coating, but inevitably impose a capacity–stability trade-off rooted in the alteration of the TM–O framework. Here, we demonstrate a synergistic strategy to construct a high-rate, air-stable P2-Na0.62K0.05MnO2/CeO2 cathode, by combining K+ bulk doping at Na sites with a CeO2 surface coating. The K+ bulk doping mitigates the Jahn–Teller effect, eliminates the low-voltage P2–P′2 transition, and converts the high-voltage P2–OP4 transition into a solid-solution reaction, while the CeO2 overlayer concurrently provides resistance to ambient air. The optimized Na0.62K0.05MnO2/CeO2 cathode delivers 67.95 mAh g–1 at 10C, retains 84.00% of its capacity after 200 cycles at 1C and 71.03% after 500 cycles at 5C, and preserves structural integrity after air exposure and water immersion. This dual-modification approach establishes Na-site doping as a design principle that decouples structural stabilization from transition-metal redox activity in P2-type oxide cathodes.