Direct Visualization of the Reversible O2−/O− Redox Process in Li‐Rich Cathode Materials
Abstract
Conventional cathodes of Li‐ion batteries mainly operate through an insertion–extraction process involving transition metal redox. These cathodes will not be able to meet the increasing requirements until lithium‐rich layered oxides emerge with beyond‐capacity performance. Nevertheless, in‐depth understanding of the evolution of crystal and excess capacity delivered by Li‐rich layered oxides is insufficient. Herein, various in situ technologies such as X‐ray diffraction and Raman spectroscopy are employed for a typical material Li1.2Ni0.2Mn0.6O2, directly visualizing O−O− (peroxo oxygen dimers) bonding mostly along the c‐axis and demonstrating the reversible O2−/O− redox process. Additionally, the formation of the peroxo OO bond is calculated via density functional theory, and the corresponding OO bond length of ≈1.3 Å matches well with the in situ Raman results. These findings enrich the oxygen chemistry in layered oxides and open opportunities to design high‐performance positive electrodes for lithium‐ion batteries.
