Enhancement of Bifunctional Effect for LiNO 3 /glyme Electrolyte by Using Dual Solvent System for Li-O 2 Batteries

Abstract

Recently, LiNO 3 -based electrolytes using tetraglyme (G4) solvent (LiNO 3 /G4) have attracted increasing attention for non-aqueous rechargeable Li-air (O 2 ) batteries (LAB) because of the bifunctional effect of NO 3 − anion as both redox mediator (RM) at air electrode and additive to form Li 2 O layer on the surface of Li metal negative electrode (NE), which suppresses Li dendrite growth and electrolyte decomposition. However, the dissociation degree of LiNO 3 salt was quite low, which causes to low ionic conductivity and the above effects of NO 3 − would not work effectively in the electrolyte. In this study, we tried to apply dual solvent system to the LiNO 3 /G4 electrolyte. Namely, acetonitrile and dimethyl sulfoxide (DMSO) with relatively high dielectric constant and low viscosity were mixed with G4 solvent to increase the number per volume and mobility of Li + and NO 3 − as carrier ions for reduction of the large overpotential during charge process and enhancement of the power density. The DMSO mixed electrolyte greatly reduced the large charge overpotential and relative stable operation for the LAB (Li ∣ O 2 ) cells. Furthermore, the Li 2 O passivation layer formed by NO 3 − anion effectively suppressed the electrolyte decomposition at Li metal NE. These effects were enhanced especially at higher rate of discharge/charge operation.