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.