Redox chemistry of LiCoO2, LiNiO2, and LiNi1/3Mn1/3Co1/3O2 cathodes: Deduced via XPS, DFT+DMFT, and charge transfer multiplet simulations

Abstract

Understanding the evolution of the physicochemical bulk properties during the Li deintercalation process is critical for optimizing battery cathode materials. In this study, we combine X-ray photoelectron spectroscopy (XPS), density functional theory plus dynamical mean-field theory (DFT+DMFT), and charge transfer multiplet (CTM) model to investigate how hybridization between transition metal (TM) 3d and oxygen 2p orbitals evolves upon Li deintercalation. Based on the presented approach combining theoretical calculations and experimental studies of pristine and deintercalated cathodes, two key aspects of ion batteries are examined: i) the detailed electronic structure and involved changes with deintercalation associated with the charge compensation mechanism, and ii) the precise experimental analysis of XPS data which are dominated by charge transfer coupled to final-state effects affecting the satellite structure. As main result for the investigated Li–TM oxides, the results indicate that the electron transfer coupled to the Li+-ion migration does not follow a rigid band model but is influenced by changes in TM 3d and O 2p states hybridization. This integrated approach suggests that 2p XPS satellite peak intensity of TM is sensitive to changes in redox chemistry, providing an indirect experimental descriptor of cathode redox behavior and guiding the design of more efficient battery materials.