Regulating the Microstructure of the Layered Oxide Cathode through the Annealing Process for High-Performance Potassium-Ion Batteries

Potassium-ion layered transition-metal oxides (K _<i>x</i> TmO₂) have gained widespread attention due to their high theoretical capacity, suitable operating voltage, and simple synthesis method. Nevertheless, the complex phase evolutions during the K⁺ intercalation/extraction process lead to poor cycling stability and rate performance, severely hindering its application in potassium-ion batteries. In this work, we found that, in addition to the temperature and heating rate, the annealing process also played a crucial role in modulating the microstructure of layered materials. Optimal annealing rate effectively helps to improve the K⁺ diffusion dynamics, thereby enhancing the electrochemical performance of the cathode. With an annealing time of 500 min (KMNM-500), the obtained sample exhibited a low-defect crystal structure and simpler phase transition process. Thus, it showed good K⁺ diffusion dynamics and cycling stability with an average capacity loss of only 0.048% per cycle at a current density of 0.5 A g^-1. Our work reveals the mechanism by which the annealing process modulates the microstructure of K _<i>x</i> TmO₂, providing guidance for the development of high-performance layered cathodes.