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-O2) batteries as it can offer an alternative way where the directly electrochemical oxidization of Li2O2 is avoided when charging, thus greatly reduce the charge overpotential. Unfortunately, the defenseless Li-metal anode would be severely corroded by the oxidized RMs that shuttle 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 as well as 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-O2 batteries with NPG membrane can offer a smooth iodine-free Li anode surface after many cycles and deliver an ultrahigh discharge capacity of ~26917 mA h g-1 at a current density of 200 mA g-1 and an ultralong cycle life (472 cycles) at 500 mA g-1 with a cutoff capacity of 500 mA h g-1, which is far better than that of the bare ones.