Solvent- and Anion-Dependent Li+-O2- Coupling Strength and Implications on the Thermodynamics and Kinetics of Li-O2 Batteries

Lithium-oxygen (Li-O2) batteries offer considerably higher gravimetric energy density than commercial Li-ion batteries (up to three times) but suffer from poor power, cycle life and round trip efficiency. Tuning the thermodynamics and pathway of the oxygen reduction reaction (ORR) in aprotic electrolytes can be used to enhance Li-O2 battery rate and discharge capacity. In this work, we present a systematic study on the role of solvent and anion on the thermodynamics and kinetics of Li+-ORR, from which we propose a unified descriptor for its pathway and kinetics. First, by thoroughly characterizing the solvation environment of Li+ ions using Raman spectroscopy, 7Li NMR, ionic conductivity and viscosity measurements, we observe increasing Li+-anion interactions with increasing anion DN in low DN solvents like DME and MeCN but minimal Li+-anion interactions in the higher DN DMSO. Next, by determining the electrolyte-dependent Li+/Li, TBA+,O2/TBA+-O2- and Li+,O2/Li+-O2- redox potentials vs the solvent-invaria...