Riveting Rubidium in Alkali-Metal Layers: High-Performance P2-Type Layered Oxide Cathodes for Potassium-Ion Batteries

Layered manganese-based oxides for potassium-ion batteries (PIBs) suffer from severe structural degradation, primarily due to irreversible phase transitions, Jahn-Teller distortion, and sluggish K+ diffusion kinetics. Here, we propose an alkali-metal site riveting strategy by selectively incorporating oversized Rb+ ions into the prismatic sites of P2-type K0.55Mn0.8Ni0.1T0.1O2. The introduced Rb+ acts as a rigid pillar, expanding the interlayer spacing and reinforcing adjacent transition-metal-oxygen (TM-O) bonds. This synergistic modulation not only widens the two-dimensional diffusion channels for rapid K+ transport but also effectively suppresses the detrimental P2-P'2 phase transition and mitigates Jahn-Teller distortion of Mn3+. Consequently, the optimized K0.55Rb0.025Mn0.8Ni0.1Ti0.1O2 cathode delivers a high reversible capacity of 105.3 mAh g-1 at a current density of 20 mA g-1, outstanding rate capability (56.1 mAh g-1 at 500 mA g-1), and long-term cycling stability with 82.1% capacity retention after 500 cycles. Furthermore, a pouch cell paired with a soft carbon anode achieves 81.3% capacity retention over 300 cycles. This work demonstrates that anchoring oversized cations in alkali-metal layers provides a universal and effective strategy toward near-zero-strain layered oxide cathodes for advanced PIBs.