A novel gel polymer electrolyte with multi-functional additive for superior ionic conductivity, stability against Li, and redox activity of lithium-air batteries

Abstract

Lithium-air batteries have the highest theoretical energy density among the rechargeable batteries. However, Li dendrite growth and the limited decomposition of discharge product, Li2O2, restrict the battery performances. In our recent study, we synthesized and utilized ammonium ionic liquid-functionalized phenothiazine (IL-PTZ) as a new redox mediator with stability against lithium to deal with these issues. Replacing liquid electrolyte to gel polymer electrolyte (GPE) is also one promising approach to enhance electrochemical performance. GPE with functional additive have been studied for improving flexibility, ionic conductivity, and chemical stability. In this study, we introduce IL-PTZ as an additive for the superior mechanical property and ionic conductivity of GPE. The elongation force of the GPE with IL-PTZ (IL-PTZ@GPE) was enhanced two times higher than that of GPE without the additive. The ionic conductivity also increased up to 1.53 × 10−3 and 4.76 × 10−3 S cm−1 at 20 and 80 °C, respectively. Furthermore, IL-PTZ molecules suppressed Li dendrite growth on the Li anode and accelerated oxygen evolution/reduction reactions on the cathode surface. IL-PTZ with only small amount of 0.1 M can act as multi-functional additive, resulting in the synergistic improvements mentioned above. As a result, Li-air cell with IL-PTZ shows superior electrochemical performances with the initial discharge capacity of 4685 mAh g− 1 and 4 times longer cyclability than the cell without additive.