Defect‐Free P2‐Type Layered K _x MnO ₂ Cathode Material for Anode‐Free Potassium‐Ion Battery

Potassium‐ion batteries (KIBs) require cathodes that combine structural robustness with fast K ⁺ transport and scalable manufacturing. Here, P2‐type KMO is developed using fast and efficient microwave heating process with controlled crystallite sizes (≈30–60 nm) and high crystallinity for Anode‐Free K‐ion batteries. In situ X‐ray powder diffraction (XRD) and Raman track reversible ‘breathing’ of the layered framework‐00l reflections shift smoothly to lower 2 θ on charge (c ≈ 12.6 → 12.8 Å) and return on discharge, with no persistent new phases‐evidence for mainly solid‐solution K ⁺ (de)intercalation. In K‐ion half‐cells, the cathode delivers 91.3 mAh g ⁻¹ with good rate capability; galvanostatic intermittent titration technique (GITT) (10 ⁻¹¹ –10 ⁻⁹ cm ² s ⁻¹ ) and electrochemical impedance spectroscopy (EIS) confirm favorable K ⁺ kinetics. Importantly, the material is further evaluated in an anode‐free K‐ion battery using carbon cloth as the current collector, achieving 83.5 mAh g ⁻¹ initially and 73.6% retention after 50 cycles with >99% Coulombic efficiency. The modest performance gap relative to half‐cells is attributed to limited K inventory and interfacial losses, indicating clear avenues for optimization. Microwave synthesis thus offers an efficient route to KMO compatible with both conventional and anode‐free operation.