A functionalized membrane for lithium-oxygen batteries to suppress the shuttle effect of redox mediators

Abstract

Redox mediators (RMs) are widely applied in lithium-oxygen (Li-O-2) batteries since they offer an alternative way to avoid the direct electrochemical oxidization of Li2O2 during charging, and thus greatly reduce the charge overpotential. Unfortunately, the defenseless Li-metal anode is severely corroded by the oxidized RMs shuttled from the cathode side, resulting in the low utilization of RMs and poor cycling stability. Herein, a functionalized double-guaranteed NPG membrane with electrostatic repulsion and steric hindrance characteristics is proposed to suppress the shuttle effect of LiI RM. Benefiting from the interaction between the O atoms in PEO and the sulfonic acid groups in Nafion and the two-dimensional skeleton structure of graphene, Nafion, PEO and graphene can couple with each other, forming a large network barrier with multi-functional properties. As expected, the LiI-based Li-O-2 batteries with the NPG membrane exhibited a smooth, iodine-free Li anode surface after many cycles and delivered an ultrahigh discharge capacity of similar to 26 917 mA h g(-1) at a current density of 200 mA g(-1) and ultralong cycle life (472 cycles) at 500 mA g(-1) with a cutoff capacity of 500 mA h g(-1), which are far better than that of the bare batteries.