Understanding interaction mechanism between δ-MnO₂ and Li₂O₂ in nonaqueous lithium-oxygen batteries

Focusing on the δ-MnO₂ acting as catalysts in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes of the cathode in nonaqueous lithium-oxygen battery, the adsorption models of key intermediates Li_xO_y on the δ-MnO₂ surface and the interface model of δ-MnO₂ and Li₂O₂ crystals are established based on density functional theory (DFT) calculations. In terms to the energy change, the δ-MnO₂ shows appropriate adsorption energy to the Li₂O₂ molecule and crystal, benefiting to the proceeding of ORR and OER processes. As for the electron distribution, the δ-MnO₂ is an indirect band gap semi-conductor, the semi-conductive characteristic is preserved after the Li_xO_y adsorption, going against the initial Li₂O₂ nucleation. During the OER process, the three-phase interface of δ-MnO₂/Li₂O₂/O₂ proves to be electronic conductive, guaranteeing the capability of combination between electrons and lithium ions. To further optimize the electronic conductivity of δ-MnO₂, the δ-MnO₂ doped with Li element, which proves to be a stable structure, is proposed to enhance the catalytic activity.