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

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 Li 2 O 2 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 ∼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. By combining steric hindrance and electrostatic repulsion, a functionalized Nafion-PEO-graphene (NPG) composite membrane was constructed and used to suppress the shuttle effect of the I − /I 3 − redox couple.