A Complete Operando Structural and Redox Perspective on the O2‐Type Lithium‐Rich Manganese Oxide LiMn 0.75 O 2

ABSTRACT Lithium‐rich materials with anionic redox are promising candidates for high‐energy‐density positive electrodes. Manganese‐based compounds like Li 2 MnO 3 offer advantages, including low toxicity and abundant resources, but suffer from poor rate capability due to irreversible oxygen loss and structural transformation. Here, we study an O2‐type layered oxide LiMn 0.75 O 2 , which shows significantly enhanced cycling stability, retaining 78% of its capacity after 140 cycles, with suppressed structural reorganization and more reversible oxygen redox. By combining electrochemical analysis with operando X‐ray absorption spectroscopy (XAS) and pair distribution function measurements (PDF), we provide a detailed picture of the material's structural and redox evolution. The first charge differs markedly from subsequent cycles, combining partially reversible bulk oxygen redox, irreversible Li extraction from surface regions, and impurities with oxygen gas release. From the second cycle onward, the reversible bulk oxygen redox process becomes progressively activated. Besides, no clear evidence of short O–O dimers are observed in PDF, suggesting a limited degree of oxygen dimerization during the oxygen redox. Overall, this work showcases the high‐capacity potential of Mn‐based Li‐rich materials, deepens understanding of their redox behavior, and underscores the power of PDF‐based operando techniques in probing local structural changes during cycling.