Surface thermodynamic stability of Li-rich Li2MnO3: Effect of defective graphene

Li-rich Mn-based cathode materials used in Li-ion batteries show ultra-high capacity due to the favorable oxygen redox behavior induced by activation of Li2MnO3. However, structural degradation associated with oxygen loss and transition metal migration occurs due to excessive oxygen redox on the surface, which is the main origin of the low coulombic efficiency, capacity fade, and voltage decay, which limit the widespread application of this high-capacity material. In this study, the underlying mechanism of tuning the surface thermodynamic stability of the Li2MnO3 model material was systematically investigated. The results showed that a defective graphene coating can effectively stabilize surface oxygen by modification of the potential energy surface, while reducing Mn migration and increasing the diffusivity of Li ions. Theoretical calculations predicted an improvement in the electrochemical performance, which was confirmed by experimental results. These findings may provide a novel strategy for increasing the surface thermodynamic stability of electrode materials.