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 O₂ , which is a typical LMRO cathode, is substantially enhanced with the help of the S^2- /SO₃ ^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 (O₂ ^2- ) are readily chemically reduced back to immobile O^2- by S^2- during charging, accompanied by the formation of SO₃ ^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.