Mechanism of Oxygen Vacancy on Impeded Phase Transformation and Electrochemical Activation in Inactive Li2MnO3

A combined experimental and computational study of an oxygen-deficient Li2MnO3−δ (δ≈0.071) cathode for understanding the role and effects of oxygen vacancies on phase transformation and electrochemical activity in Li-ion batteries is presented. The oxygen-deficient Li2MnO3−δ exhibits improved electrochemical reactivity toward Li+ ions without significant loss of structural stability. The oxidation of O during Li+ ion extraction can be suppressed by the enhanced redox reaction of Mn in this material. Furthermore, the inevitable phase transformation of Li2MnO3 can be impeded by the increased kinetic barriers to Mn migration in Li2MnO3−δ (ΔEbarrier=1.0–2.5 eV), which disfavors the formation of stable intermediate coordination geometries due to the oxygen vacancies. These findings reveal the underlying mechanism on the role of the oxygen vacancies in changing phase transformation and electrochemical activity in inactive Li2MnO3, and provide a scientific insight to the electrochemical reactivity and sustainability of Li-rich oxide cathode materials in Li-ion batteries.