Enabling reversible phase transition on K5/9Mn7/9Ti2/9O2 for high-performance potassium-ion batteries cathodes

The development of PIBs is challenged by the availability of suitable cathode materials capable of stably hosting the large-sized K+, whose continuous intercalation/deintercalation in the crystalline framework will cause serious phase deformation and irreversible structure degradation. Here, we demonstrated the possibility of achieving a highly reversible potassiation/depotassiation process in a layered metal oxide of K5/9Mn7/9Ti2/9O2. We confirmed that the existence of Ti can effectively combat the transition metal slab gliding of the P2-type structure during the electrochemical reaction. The destructive P2-O2 phase transition was efficiently diminished even when charged to a high voltage of 4.2 V, instead forming a stable OP4 phase which was able to switch back to its pristine P2-type structure upon discharge, accordingly providing an improved electrochemical performance of PIBs. We expect that the discovery and fundamental understanding of such a reversible P2-OP4 phase transition provide insights in the structural design of PIBs cathodes.