Multiphase Riveting Structure for High Power and Long Lifespan Potassium-Ion Batteries

The development of potassium-ion batteries (KIBs) relies on the exploration of stable layer-structured oxide cathode materials and a comprehensive understanding of ion storage and diffusion behaviors. A multiphase riveting-structured O3/P2/P3-Na0.9[Ni0.3Mn0.55Cu0.1Ti0.05]O2 (Tri-NMCT) is employed as cathode material for KIBs. It demonstrates an initial discharge specific capacity of 108 mA g-1 at current density of 15 mA g-1 in the voltage range of 1.5-4 V. Excellent cyclic stability is exhibited as well with a high 83% capacity retention after 600 cycles at a higher current density of 300 mA g-1. Based on the in-situ XRD, it reveals that the P2 phase offers a more stable triangular prism site compared to the O3 phase. This stability inhibits the undesired phase transition from P3 to O3 during discharge, thereby ensuring the long-term cyclic performance. Furthermore, Density of state (DOS) calculations and migration barrier analyses indicate a preferential migration of K+ ions to the P2 phase due to the lower Fermi level. This observation elucidates the structural preservation of the P3 phase during K+ embedding. Overall, this work sheds light on Tri-NMCT as a promising cathode material for advanced KIBs.