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

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.