Synergy between LiNO3 and Tetraglyme-Sulfone Dual-Solvent Electrolyte Solutions in Li-O2 Batteries

Abstract

LiNO3 has been widely studied as a redox mediator to reduce positive electrode overvoltage during charging of lithium/air (O2) batteries. LiNO3 has a bifunctional effect as a redox mediator for the positive electrode and as a surface modifier for the lithium negative electrode. The dissociation of LiNO3 electrolyte salt was enhanced by using a mixed solvent of tetraglyme and a sulfone with a high dielectric constant. This extended the charging voltage plateau because the mixed solvent enhanced the oxidation of into NO2 in the 1.0 M LiNO3 electrolyte solution. The viscosities of the sulfone-containing electrolyte solutions decreased and their ionic conductivities increased as the temperature increased. Therefore, Walden plots for the electrolyte solutions containing sulfones were parallel to the ideal line, meaning that the dissociation of LiNO3 was unaffected by temperature due to the strong solvation of ethyl methyl sulfone and tetramethylene sulfone to Li+ ions. Consequently, the sulfone-containing electrolyte solutions delivered better charging performance than an electrolyte solution of simple tetraglyme at 50 °C.