Highly selective metal-organic framework-based (MOF-5) separator for non-aqueous redox flow battery

Non-aqueous redox flow batteries (NARFBs) are promising in the grid-scale energy storage for the harvesting of the intermittent renewable power sources. However, the lack of efficient separator is still impeding their further development. A flexible nanoporous separator is prepared through a “rolling dough” strategy, with zinc metal-organic framework (MOF-5) and polytetrafluoroethylene as the substrate. The prepared separator shows a remarkable ionic selectivity of Li⁺ over N-(ferrocenylmethyl)-N,N-dimethyl-N-ethylammonium ions (Fc1N112⁺) at a high ratio 26.6. A Li-based hybrid NARFB constructed with the separator exhibits substantially high Coulombic efficiency 99.7% and average discharge capacity 2.26 Ah L⁻¹ with capacity retention 99.96% per cycle over 200 cycles at 4 mA cm⁻². The excellent performance is attributed to the MOF nanoparticles and the designed composite structure, which achieves both high ionic selectivity and chemical stability simultaneously. This work provides a facile and efficient strategy to fabricate high-performance separator for NARFBs.