Competition between Metal Dissolution and Gas Release in Li-Rich Li₃Ru_yIr_1–yO₄ Model Compounds Showing Anionic Redox

Li-ion batteries have experienced tremendous progress over the past decade; however, their energy density should still be increased to power electric vehicles. Following this aim, the energy density of the cathode material can be drastically increased by making use of anionic redox, although it often comes along with material degradation. In this study, through a detailed analysis of the charge compensation mechanism of Li3RuO4 by online electrochemical mass spectrometry, X-ray absorption spectroscopy, and ultraviolet spectroscopy, we unveiled a new degradation mechanism for a cathode material showing anionic redox, namely the dissolution of Ru forming RuO4/RuO4– species with limited release of gas from the material. We show that this dissolution can be effectively tackled by substituting Ru with Ir. However, such a strategy leads to a massive increase in the release of O2 gas at the end of the charge. Density functional theory calculations prove that the relative stability of the end members RuO4 and IrO4 versus oxygen release is at the origin of this competition between metal dissolution and gas release.