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 Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 , which is a typical LMRO cathode, is substantially enhanced with the help of the S 2- /SO 3 2- 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 (O 2 2- ) are readily chemically reduced back to immobile O 2- by S 2- during charging, accompanied by the formation of SO 3 2- , which plays a critical role in stabilizing the oxygen lattice and eventually inhibiting the release of oxygen. More importantly, the S 2- 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.