Thermodynamically Favoured Bulk O2 Formation on Charging in LiCoO2 and LiNiO2 Cathode Materials

The formation of O2 molecules within the bulk of LiCoO2 and LiNiO2 cathode materials during charging has been reported experimentally, but the validity and significance of these observations remain debated. Using density functional theory calculations, we demonstrate that at high states of charge, layered LiNiO2 and LiCoO2 are thermodynamically unstable with respect to both O2 gas release and internal decomposition forming bulk-confined O2 molecules, indicating that, from a thermodynamic perspective, the oxygen chemistry of these stoichiometric layered oxides parallels that of Li-rich oxides, and may likewise limit their long-term cycling stability.