Achieving Reversible Anionic Redox via Homogeneous Transition Metal‐Oxygen Coordination in Li‐Rich Layered Oxides

ABSTRACT Li‐rich layered oxides (LLOs) are promising high‐capacity cathode materials for next generation Li‐ion batteries, but their practical application is hindered by voltage decay and capacity fading, which primarily originate from irreversible oxygen behaviors. Given that transition metal‐oxygen (TM─O) bonding is crucial for stabilizing anionic redox, this study reveals the critical role of elemental composition in determining the homogeneity of the TM‐O coordination environment within LLOs. This homogeneity directly influences the electrochemical behavior and structural stability of the material. Combining in situ X‐ray diffraction (XRD) and density‐functional theory (DFT) calculations on various model compounds, we demonstrate that while Co thermodynamically enhancing the Mn─O bonds, it forms highly covalent Co─O bonds that disrupt the uniformity of the TM─O bonding network. This inhomogeneity kinetically promotes irreversible ligand‐to‐metal charge transfer, exacerbates lattice strain along c ‐axis, and accelerates oxygen loss. In contrast, Ni promotes a homogeneous TM‐O coordination environment, facilitating reversible charge compensation and accommodating lattice strain through gentle ab ‐plane expansion. Consequently, the Ni‐rich cathodes achieve superior cycling stability and voltage retention. Our findings establish that a uniform TM─O bonding network is more crucial than the absolute bond strength for achieving reversible anionic redox, providing a new design principle for stable and high‐energy cathode materials.