Surface residual alkali reverse utilization: Stabilizing the lay-structured oxide cathode for high stability potassium ion batteries

Manganese base oxide is considered as a promising cathode material for potassium ion batteries (PIBs). However, the continuous phase transition leads to the poor stability of surface structure and its cycle life still cannot meet the increasing requirements. At the same time, because of its thermodynamic instability, residual alkali will precipitate with the increase of potassium content or exposure to humid environment, which seriously affects its performance. Surface engineering techniques are thus employed herein to modify the active material surface structure by growing a protective perovskite-type KTaO3 layer reversely utilizing the surface residual alkali as potassium resource. The obtained K0.5MnO2@KTaO3 composite exabits a superior cycling lifespan keeping the capacity retention high to 98.8 % after 200 cycles at 300 mAh/g. Besides increasing the environmental adaptability, the protective perovskite-type KTaO3 layer can not only inhibit the dissolution of transition metals by stabilizing the surface crystal structure, but also accelerate the K+ diffusion by decreasing the interface activation energy between cathode and electrolyte.