A MOF-Gel Based Separator for Suppressing Redox Mediator Shuttling in Li-O2 Batteries.

ABSTRACT

Redox mediators (RMs) are widely utilized in the electrolytes of Li-O2 batteries to catalyze the formation/decomposition of Li2O2, which significantly enhances the cycling performance and reduces the charge overpotential. However, RMs have a shuttle effect by migrating to the Li anode side and inducing Li metal degradation through a parasitic reaction. Herein, a metal-organic framework gel (MOF-gel) separator is proposed to restrain the shuttling of RMs. Compared to traditional MOF nanoparticles, MOF gels form uniform and dense films on the separators. When using Ru(acac)3 (ruthenium acetylacetonate) as an RM, the MOF-gel separator suppresses the shuttling of Ru(acac)3 toward the Li anode side and significantly enhances the performance of Li-O2 batteries. Specifically, Li-O2 batteries exhibit an ultralong cycling life (410 cycles) at a current density of 0.5 A g-1. Moreover, the batteries using the MOF-gel/celgard separator exhibit significantly improved cycling performance (increase by ≈1.6 times) at a high current density of 1.0 A g-1 and a decreased charge/discharge overpotential. This result is expected to guide future development of battery separators and the exploration of redox mediators.