Metastability and Reversibility of Anionic Redox-Based Cathode for High-Energy Rechargeable Batteries
Bao Qiu, Minghao Zhang, Seung-Yong Lee, Haodong Liu, Thomas A. Wynn, Lijun Wu, Yimei Zhu, Wen Wen, Craig Brown, Dong Zhou, Zhaoping Liu, Ying Shirley Meng
Great focus has been placed on the advancement of anionic redox, to which Li-rich layered oxide cathodes high capacities - currently exceeding 300 mAh g-1 - are attributed. With almost doubled capacity compared with present cathode materials, performance of Li-rich layered oxides are still short of commercial expectations after over a decade of academic efforts. The practical issues of this group of materials originate from irreversible structure transformation and voltage decay upon cycling-processes in which defect electrochemistry plays a vital role. Understanding the correlation between defect generation and voltage decay is essential for implementing rational design strategies to improve cycling stability in this class of materials. Here we demonstrate the unique metastable structure of cycled Li-rich layered oxide resulting from defect formation. Mild head treatment can be applied to cycled material to drive the system back to a stable state and subsequently lead to the voltage recovery. This study of structure metastability and reversibility opens up new opportunities for resolving the voltage decay issue in high-capacity layered oxides with anionic redox activities.