Understanding of electrochemical K+/Na+ exchange mechanisms in layered oxides

Ion-exchange reactions are commonly used to develop novel metastable electrode materials for alkali-ion batteries that cannot be synthesized using direct chemical reactions. In this study, the electrochemical K Na ion-exchange reaction mechanisms in a layered KxCoO2 cathode as model system were investigated operando and ex situ structure characterization techniques. Some level of ions was observed remain during Interestingly, well separated from Na-rich phases discharged state, they form an intermediate phase which mixed at top charge. We discovered such residual prevent collapse high-voltage regime, thereby improving cycling stability Na-battery system.