Imidazolium bromide: A tri-functional additive for rechargeable Li-O2 batteries

High energy density lithium-oxygen (Li-O2) batteries require soluble catalysts to accelerate the kinetics of oxygen reduction/evolution reaction (ORR/OER), and require SEI forming additives to protect lithium metal anode from side reaction with solvents, reduced oxygen species and soluble catalysts. In this study, a tri-functional additives 1-methyl, 3-benzyl, 1H imidazolium bromide (IMPBr) is dissolved in the dimethyl sulfoxide (DMSO)-based electrolyte to solve the problems of the slow dynamic process of ORR and OER, and protect the lithium anode by suppressing the dendrite formation in O2 atmosphere. During discharging, IMP+ has a strong binding ability to the intermediate product O2−, and Br− is highly associated with Li+, helping drive the solvation mechanism. During charging, Br− mediates the decomposition of battery discharge products and reduces the charge overpotential. Meanwhile, the positively charged IMP+ can be attracted to the surface of the anode via electric attraction, in situ forming a stable SEI layer to prevent DMSO, Br3–, and Br2 from attacking the lithium metal and growth of lithium dendrites. The synergy effect of the IMP+ and Br– improves the cycle and rate performance of the Li-O2 battery.