Phase Engineering and Ion Diffusion Kinetics for High Power and Long Lifespan Potassium-Ion Batteries

The exploration of stable layered oxide cathode materials is crucial for advancing potassium-ion batteries (PIBs) technology and understanding ion storage and diffusion behaviors. P2-Na0.6[Ni0.3Mn0.55Cu0.1Ti0.05]O2 (P2-NMCT) is explored as a cathode material for PIBs. Operating within the voltage range of 1.5–4 V, it demonstrates an initial discharge capacity of 96 mAh g–1 at a current density of 15 mA g–1. Under a high current density of 300 mA g–1, it exhibits 83.0% capacity retention after 500 cycles, highlighting exceptional cycling stability. Based on the in situ X-ray diffraction and galvanostatic intermittent titration technique analyses, it is observed that during the Na+/K+ exchange process, potassium ions enrich to form a potassium-rich P2 phase, while residual sodium ions maintain the original sodium-rich P2 phase structure. This biphasic structure and directed ion migration contribute to excellent kinetic performance. Additionally, in the later stages of discharge, the enriched region is disrupted, leading to the formation of a low-strain P2Na/K phase with a mixed Na/K distribution in the alkali metal layers. This transformation stabilizes the structural integrity and enhances the cycling stability, showcasing its potential as a high-performance cathode material for PIBs.