Experimental and Computational Analysis of the Solvent-Dependent O2/Li+-O2− Redox Couple: Standard Potentials, Coupling Strength, and Implications for Lithium-Oxygen Batteries

Understanding and controlling the kinetics of O2 reduction in the presence of Li+‐containing aprotic solvents, to either Li+‐O2− by one‐electron reduction or Li2O2 by two‐electron reduction, is instrumental to enhance the discharge voltage and capacity of aprotic Li‐O2 batteries. Standard potentials of O2/Li+‐O2− and O2/O2− were experimentally measured and computed using a mixed cluster‐continuum model of ion solvation. Increasing combined solvation of Li+ and O2− was found to lower the coupling of Li+‐O2− and the difference between O2/Li+‐O2− and O2/O2− potentials. The solvation energy of Li+ trended with donor number (DN), and varied greater than that of O2− ions, which correlated with acceptor number (AN), explaining a previously reported correlation between Li+‐O2− solubility and DN. These results highlight the importance of the interplay between ion–solvent and ion–ion interactions for manipulating the energetics of intermediate species produced in aprotic metal–oxygen batteries. The free‐energy landscape of reactions involved in the Li oxygen reduction reaction (ORR) were obtained by rotating ring disk (RRD) measurements and calculations. Differences in redox potentials of O2/O2− and O2/Li+‐O2− couples vs. Li+/Li in dimethoxyethane (DME) and dimethylsulfoxide (DMSO) reflect the influence of increasing solvation on the free energy of O2− formation vs. Li+/Li and Li+‐O2− coupling.