Stabilizing Anionic Redox Chemistry in a Mn‐Based Layered Oxide Cathode Constructed by Li‐Deficient Pristine State

Abstract Li‐rich cathode materials are of significant interest for coupling anionic redox with cationic redox chemistry to achieve high‐energy‐density batteries. However, lattice oxygen loss and derived structure distortion would induce serious capacity loss and voltage decay, further hindering its practical application. Herein, a novel Li‐rich cathode material, O3‐type Li 0.6 Li 0.2 Mn 0.8 O 2 , is developed with the pristine state displaying both a Li excess in the transition metal layer and a deficiency in the alkali metal layer. Benefiting from stable structure evolution and Li migration processes, not only can high reversible capacity (≈329 mAh g −1 ) be harvested but also irreversible/reversible anionic/cationic redox reactions are comprehensively assigned via the combination of in/ex situ spectroscopies. Furthermore, irreversible lattice oxygen loss and structure distortion are effectively restrained, resulting in long‐term cycle stability (capacity drop of 0.045% per cycle, 500 cycles). Altogether, tuning the Li state in the alkali metal layer presents a promising way for modification of high‐capacity Li‐rich cathode candidates.