Probing Oxygen Activity in Li-Rich Cathodes with Core-Level Spectroscopy*

It is commonly recognized that utilization of oxygen redox is an intriguing route for obtaining higher capacity in Li-ion batteries (LIBs). Despite numerous experimental and theoretical studies attempting to unravel the electronic origin of oxygen redox behavior, whether the oxidation of oxygen occurs via the formation peroxo-like species or depletion of electrons from the non-bonding states is still, however, an open question, and it is unclear how the electron-depleted oxygen states manifest themselves under spectroscopic observations. In this study, using the Li-rich Li₅FeO₄ as a model system, we performed ab-initio Molecular Dynamics (AIMD) simulations to investigate the structural response of oxygen matrix to delithiation. The oxygen K-edge X-ray absorption near-edge spectra (XANES) were modeled using Bethe-Salpethe Equation (BSE) approach and compared with experiments, from which the oxygen redox mechanism is uncovered.