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

Abstract

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 LixOy 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 LixOy 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.