Phase Engineering\nand Ion Diffusion Kinetics for High\nPower and Long Lifespan Potassium-Ion Batteries

The exploration of stable layered oxide cathode materials\nis crucial\nfor advancing potassium-ion batteries (PIBs) technology and understanding\nion storage and diffusion behaviors. P2-Na<sub>0.6</sub>[Ni<sub>0.3</sub>Mn<sub>0.55</sub>Cu<sub>0.1</sub>Ti<sub>0.05</sub>]O<sub>2</sub> (P2-NMCT)\nis explored as a cathode material for PIBs. Operating within the voltage\nrange of 1.5–4 V, it demonstrates an initial discharge capacity\nof 96 mAh g<sup>–1</sup> at a current density of 15 mA g<sup>–1</sup>. Under a high current density of 300 mA g<sup>–1</sup>, it exhibits 83.0% capacity retention after 500 cycles, highlighting\nexceptional cycling stability. Based on the in situ X-ray diffraction\nand galvanostatic intermittent titration technique analyses, it is\nobserved that during the Na<sup>+</sup>/K<sup>+</sup> exchange process,\npotassium ions enrich to form a potassium-rich P2 phase, while residual\nsodium ions maintain the original sodium-rich P2 phase structure.\nThis biphasic structure and directed ion migration contribute to excellent\nkinetic performance. Additionally, in the later stages of discharge,\nthe enriched region is disrupted, leading to the formation of a low-strain\nP2<sub>Na/K</sub> phase with a mixed Na/K distribution in the alkali\nmetal layers. This transformation stabilizes the structural integrity\nand enhances the cycling stability, showcasing its potential as a\nhigh-performance cathode material for PIBs.