Oxygen Loss on Disordered Li-Excess, Mn-Rich Li-Ion Cathode Li2MnO2F through First-Principles Modeling

Oxygen evolution energies were calculated for the {100}, {110}, {111}, and {112} type facets of the rock-salt-structured cation-disordered Li-excess, Mn-rich Li-ion (DRX) cathode Li2MnO2F at the fully lithiated, 25% delithiation, and 50% delithiation states. Our calculations showed that Li2MnO2F remains much more robust to O loss than its nonfluorinated counterparts, as has been shown in experimental work. In particular, the {110} and {112} facets are the most resilient against O loss. Focusing on the {100} type facet, which previous work has shown to be the most likely exposed facet of Li2MnO2F, it was found that higher proportions of Li in an O coordination shell lead to lower O evolution energy (ẼO) and facilitate O loss. It was also found that at higher states of delithiation, surface fluorine had a weaker effect in increasing ẼO, meaning the protective effect of F against O loss is more effective at higher lithiation states. Electronic structure chemical bonding analysis revealed weaker bonding interactions between Li and O correlated with lower ẼO and hence a higher propensity for surface O loss.