The study of different redox mediators for competent Li–air batteries

Abstract

Li-air batteries attract abundant attention in recent years with superior performance, and have largely replaced traditional methods of energy storage. The main objective of Li–air battery is to provide long-range electric-vehicles, while functioning as an environmentally friendly and compact energy storage solution. They offer the highest theoretical energy density (3500 Wh/kg), almost 20% higher than the ordinary Li-ion batteries. Nonetheless, Li-air batteries still face numerous issues, the most serious of which are high overpotential and parasitic reactions. Several redox mediators (RM) have been studied in order to reduce the high overpotential and the influence of side reactions. RM function in the electrolyte as soluble catalysts, limiting the formation of singlet oxygen while promoting the formation of discharge product Li2O2. This research primarily focuses on the optimization of Li-air cells with different redox mediators in conjunction with appropriate electrolyte, as a result reducing overpotential, parasitic byproducts and increasing efficiency. Under standard electrolytic conditions, ruthenocene exhibits high stability by completing 83 cycles, thus outperforming the other mediators being investigated. Further, di-tert-butyl-1,4-benzoquinone is more commonly used for discharge reaction and has been shown to increase the capacity of Li–O2 batteries by 80 times. This study reconfirms lithium bis(trifluoromethylsulfonyl) imide in tetraethyleneglycol dimethylether as the most stable electrolyte.