Effects of aqueous electrolytes on the voltage behaviors of rechargeable Li-air batteries

Abstract

Aqueous Li-air batteries have attracted a great deal of attention due to their high theoretical energy capacities. However, while still in the early stages of research, the reported energy capacities of Li-air batteries are far from what has been theoretically predicted. In this research, we have designed a Li-air battery that has a Li ǀ organic liquid electrolyte ǀ Li+-conducting glass ceramic plate (LiGC plate) ǀ aqueous electrolyte ǀ Pt air electrode structure and studied the impacts of the compositions of the aqueous electrolyte on the battery performance. With lower concentrations of alkali aqueous electrolytes (≤0.05M LiOH), a discharge voltage of approximately 3.5V (at 0.05mAcm−2) and a voltage efficiency up to 84% were observed. The addition of LiClO4 into the aqueous solution slightly lowered the discharge voltage to 3.3V but dramatically decreased the internal resistance of the battery to 35.4Ωcm−2. With a charge voltage plateau observed at 3.90V at a current of 0.05mAcm−2, the Li ǀ organic liquid electrolyte ǀ LiGC ǀ 1M LiClO4 ǀ Pt air battery showed an 85% voltage efficiency at room temperature. Adding LiClO4 into the aqueous electrolytes resulted in an impedance reduction and slowed the pH increase of the alkaline-based electrolyte due to the fast or long-term discharge of the air electrode in the Li-air battery. The discharge and charge voltage behaviors of the battery and the changes to the pH values of the aqueous electrolyte at different current rates were also recorded and are presented in this paper.