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 Li1.2 Ni0.13 Co0.13 Mn0.54 O2 , which is a typical LMRO cathode, is substantially enhanced with the help of the S2- /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 O2- by S2- 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 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.
Keywords: Li- and Mn-rich layered oxides; anionic redox; lithium-ion batteries; oxygen release; redox couples.
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