Enhancing the Reaction Kinetics and Reversibility of Li-O2 Batteries by Multifunctional Polymer Additive

As a potential candidate for next-generation energy storage systems, Li-O-2 batteries (LOBs) with their attractive theoretical energy density have triggered great interest. However, tough issues of sluggish oxygen reduction reaction/oxygen evolution reaction (ORR/OER) kinetics, poor rechargeability, superoxide-derived side reactions, and Li-metal corrosion in LOBs limit their practical applications. Herein, a poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) additive is introduced into the typical electrolyte, giving superior cycling performance to LOBs. Enabling strong solvation of Li+, PTFEMA regulates a uniform Li+ flow at the cathode and anode sides of LOBs. Induced by homogeneous Li+ flux and favorable adsorption with superoxide species, PTFEMA promotes superoxide transformation in the ORR and inhibits superoxide-induced parasitic reactions. Uniform Li+ flux gives evenly-distributed Li2O2 that can be completely decomposed during OER. In addition, PTFEMA protects Li-metal against corrosion from O-2, superoxide, and byproducts shuttle. Hence, accelerated ORR/OER kinetics, facilitated rechargeability, suppressed superoxide-derived side reactions, and well-protected Li-metal can be simultaneously realized with PTFEMA, resulting in significantly enhanced electrochemical performance of LOBs. This electrolyte engineering involving facile multifunctional polymer additives provides a practical alternative to complex componential optimization toward commercial LOBs and gives insight to the understanding of uniform Li+ flux on reaction kinetics and reversibility.