A General Chemical Prepotassiation Strategy for Boosting the Zn-Storage Performance of Polymorphic MnO₂ Cathodes

Ion pre-intercalation engineering, particularly using large-radius K⁺ cations, is pivotal to overcome the sluggish Zn²⁺ diffusion kinetics and severe structural instability issues that limit MnO₂ 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 MnO₂ 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 Zn²⁺ transport kinetics and reinforcing the MnO₂ framework stability. Consequently, the optimized α-K_0.05MnO₂ 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-MnO₂ (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.