Direct Observation of Solvent Donor Number Effect on Lithium–Oxygen Battery Capacity via a Nanoarray Cathode Model

The solvent properties are critical factors that strongly influence the capacities and cycle lives of lithium–oxygen (Li–O2) batteries. In previous studies of solvent effects, disk electrodes are prototypes far from practical application while practical composite electrodes are interfered by additives. Herein, we propose MnO2 nanoarrays as a cathode model to directly observe the effect of the tunable donicity of dimethyl sulfoxide (DMSO)–tetra (ethylene glycol) dimethyl ether (G4) binary solvent. The facilely prepared MnO2 nanoarrays on carbon clothes not only mimic carbon-supported catalysts but also provide an open architecture that helps distinguish discharge products from complex electrodes without further characterizations. Using nanoarray models, this work directly observes the morphologies of discharge products that gradually evolve from conformal films to toroid-like particles with the increase in the DMSO ratio in the binary solvents. Thus, the Li–O2 battery capacities are proportional to the donicities of the binary solvents. However, the reactive solvent that provides high donicity greatly deteriorates the cycle performance. A compromise should be achieved between capacity and stability when tuning the donicity of the binary solvent. The novel nanoarray model and fundamental findings in this work will further help the electrolyte optimization for Li–O2 batteries.