A General Chemical Prepotassiation Strategy for Boosting the Zn‐Storage Performance of Polymorphic MnO ₂ Cathodes

ABSTRACT Ion pre‐intercalation engineering, particularly using large‐radius K + cations, is pivotal to overcome the sluggish Zn 2+ diffusion kinetics and severe structural instability issues that limit MnO 2 cathodes for AZIBs. However, conventional pre‐intercalation methods typically rely on hydrothermal or calcination under harsh high‐temperature/pressure conditions, which compromise scalability, phase purity, and stoichiometric control. Herein, we propose a mild chemical prepotassiation strategy, that employs 9‐fluorenone potassium (FL‐K) as a highly reactive K + /e − donor, to enable rapid and quantitative K + insertion into diverse MnO 2 polymorphs ( α ‐, γ ‐, and δ ‐phases) in just 30 s under ambient conditions. The pre‐intercalated K + ions act as robust structural pillars that simultaneously enlarge the tunnel/interlayer spacing and enhance electronic conductivity, thereby dramatically accelerating Zn 2+ transport kinetics and reinforcing the MnO 2 framework stability. Consequently, the optimized α ‐K 0.05 MnO 2 cathode delivers superior rate capability (97.5 mAh g −1 at 10C) and cycling durability (64.5% retention after 300 cycles at 3C), far surpassing pristine α ‐MnO 2 (merely 25.6 mAh g −1 and 38.5% retention). This efficient strategy, characterized by near‐100% atomic utilization and full reagent recyclability, establishes a sustainable and universal prepotassiation protocol for engineering high‐performance intercalation‐type electrode materials.