Dissociative adsorption of H2O on LiCoO2 (00l) surfaces: Co reduction induced by electron transfer from intrinsic defects.

Abstract

Understanding the mechanism of the interaction of lithium ion conductors with water is crucial for both fundamental and technological points of view. Despite the generally accepted fact that water is one of main sources of the degradation of Li-ion recharge batteries, the physicochemical processes occurring at the water-lithium ion conductor interface are not fully understood. By using synchrotron X-ray photoelectron spectroscopy (SXPS) and O K- and Co L- X-ray absorption near edge structure (XANES), we evidence that H2O is dissociatively adsorbed on LiCoO2 thin film at room temperature resulting in the formation of OH groups and the accumulation of the negative charge at the surface accompanied by electron transfer to the initial empty Co3d (eg (*)) state. By considering the experimentally obtained energy diagram of the ionic conductor and water, direct charge transfer is not favorable due to a high difference in the chemical potential of the ionic conductor and electronic levels of the molecule. Here, we develop the model for the dissociative water adsorption which explains the electron transfer to LiCoO2 by using the atomistic approach. The model takes into account the intrinsic defects found on the surface (<2 nm depth) by using the depth resolved photoemission experiments and can be explored to other layered transition metal oxides to interpret the interaction of water with the surface of ionic conductors.