Elucidating the Oxygen Reduction Reaction Kinetics and the Origins of the Anomalous Tafel Behavior at the Lithium–Oxygen Cell Cathode

Development of Li–O2 cells, potentially providing ∼3 times the capacity of Li-ion cells, depends on a fundamental understanding of the oxygen reduction reaction (ORR) at the cathode. The present study investigates the mechanism and kinetics of the oxygen reduction reaction (ORR) on a glassy carbon (GC) electrode in an oxygen saturated solution of 0.1 M lithium bis-trifluoromethanesulfonimidate (LiTFSI) in 1,2-dimethoxyethane (DME) using cyclic voltammetery (CV) and the rotating ring-disk electrode (RRDE) technique. A reaction scheme considering disproportionation of LiO2 on both the cathode surface and the electrolyte bulk to form Li2O2 was proposed, and the RRDE measurements, in conjunction with an electrochemical kinetics model, were used to calculate the corresponding rate constants. The surface disproportionation reaction was found to dominate the kinetics of the ORR, and the model could explain experimental observations regarding the cell discharge products. Further, the widely reported anomalous Taf...