A Redox Couple Strategy Enables Long‐Cycling Li‐ and Mn‐Rich Layered Oxide Cathodes by Suppressing Oxygen Release

Li‐ and Mn‐rich layered oxides (LMROs) are considered the most promising cathode candidates for next‐generation high‐energy lithium‐ion batteries. The poor cycling stability and fast voltage fading resulting from oxygen release during charging, however, severely hinders their practical application. Herein, a strategy of introducing an additional redox couple is proposed to eliminate the persistent problem of oxygen release. As a proof of concept, the cycling stability of Li1.2Ni0.13Co0.13Mn0.54O2, which is a typical LMRO cathode, is substantially enhanced with the help of the S2−/SO32− redox couple, and the capacity shows no decay with a retention of 100% after 700 cycles at 1C, far superior to the bare counterpart (61.7%). The surface peroxide ions (O22−) are readily chemically reduced back to immobile O2− by S2− during charging, accompanied by the formation of SO32−, which plays a critical role in stabilizing the oxygen lattice and eventually inhibiting the release of oxygen. More importantly, the S2− ions are regenerated during the following discharging process and participate in the chemical redox reaction again. The findings shed light on a potential direction to tackle the poor cycling stability of high‐energy anion‐redox cathode materials for rechargeable metal‐ion batteries.