Unveiling the mechanism of charge compensation in Li2RuxMn1_xO3 by tracking atomic structural evolution

The relationship between the structural evolution and redox of Li-rich transition-metal layered oxides (LLOs) cathodes remains ambiguous, obstructing the development of high-performance lithium-ion (Li+) battery. Herein, the coherent effects of local atomic and electronic structure in Li2RuxMn1_xO3 (LRMO) with a wide voltage window (1.3-4.8 V) is identified by in situ X-ray absorption fine spec-troscopy (XAFS) and chemometrics. We not only skillfully separated the redox active structures to track the electrochemical path, but also visualized the coupling mechanism between the evolution of Ru-Ru dimer and the (de) excitation of cations and anions. Furthermore, introducing manganese triggers the "heterogeneity" of coordination environment and electronic structure between Ru and Mn after dis-charge to 3 V. The change of thermodynamic and kinetic paths affects the relithiation, and further leads to the hysteresis of the anion activation structure relaxation of Li2Ru0.4Mn0.6O3 relative to Li2RuO3 (LRO). Additionally, it is demonstrated that the high charge cut-off voltage restrains the relaxation of anionic active structure in LRO from a new perspective through comparative experiments. Our work associates the evolution of atomic structure with charge compensation and negative electrochemical reactions such as voltage hysteresis (VH) and capacity attenuation, deepening the understanding electrochemical reac-tion mechanism of LLOs during the first cycle and providing a theoretical support for the further design and synthesis of high-efficiency cathodes.(c) 2022 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press.