Structural metastability and reversibility in anionic redox-based cathode for next generation rechargeable battery

Great focus has recently been placed on the advancement of anionic redox, to which high capacities of Li-rich layered oxides are attributed. With almost doubled capacity compared with state-of-the-art cathode materials, Li-rich layered oxides still fall short in other performance metrics. Among these, gradual voltage decay upon cycling remains the most hindering obstacle, in which defect electrochemistry plays a critical role. Here, we reveal the metastable state of cycled Li-rich layered oxide which stems from structural defects in different dimensions. We demonstrate the unique cycled metastable structure concomitant with anionic redox activity is responsible for the voltage decay. More importantly, through mild thermal energy, the metastable state can be driven to a stable state close to the pristine state, bringing about structural and voltage recovery. These insights elucidate understanding the structure metastability and reversibility is essential for implementing rational design strategies to improve cycling stability for high-capacity layered oxides.