Enabling Facile Anionic Kinetics through Cationic Redox Mediator in Li-Rich Layered Cathodes

Anionic oxygen redox has aroused great interest in developing high-capacity Li-ion battery cathode materials. The fundamental understanding of this concept, compared to cationic redox, has promoted extensive studies on lithium transition metal oxides including those of 4d and 5d transition metals. Lithium ruthenium oxide has been found to exhibit a reversible anionic redox upon cycling. However, lithium-rich layered oxide with anionic redox is still facing great challenges, such as sluggish kinetics. Here we investigate the effect of cationic redox reaction on the kinetics of anionic reaction when they are strongly coupled. We report the cobalt-substituted lithium ruthenium oxide, where all Ru, Co, and O redox participate in the charge compensation mechanism in relatively defined voltage regions. The improved anionic kinetics is attributed to the fast cationic Co redox process that serves as a redox mediator. Our work sheds light on the potential direction to address the commonly believed sluggish anionic kinetics in high-capacity oxygen-redox cathode materials.