Ambivalent Effect of Oxygen Vacancies on Li2MnO3: A First-Principles Study

First-principles calculations were done to examine the effect of oxygen vacancies in Li2MnO3 on the lithium extraction from the crystal. As the ratio of O-vacancy increases, the redox potential associated with the lithium extraction decreases and the Mn contribution in the charge compensation for the lithium extraction increases. These findings indicate that the introduction of O-vacancy activates the Mn sites as the redox center in the lithium extraction process. However, the lithium extraction from Li2MnO3 tends to cause successive O2 evolution from the crystal. This results in a high O-vacancy density in the crystal, which in turn triggers a drastic volume reduction during the lithium extraction process.