Ion sieve membrane: Homogenizing Li flux and restricting polysulfides migration enables long life and highly stable Li-S battery.

Limited by the notorious Li dendrites growth and serious polysulfide shuttle effect, the development of lithium-sulfur (Li-S) batteries is stagnant. Herein, a multifunctional separator composed of Cu-based metal-organic framework (Cu-MOF) and Li-Nafion was proposed to address the above intractable issues. The Cu-MOF with homogeneous porous structure and abundant Lewis acidic sites not only promotes uniform Li flux, but also exhibits a strong chemical interaction with polysulfides to inhibit the shuttle effect. Moreover, the narrow pore size distribution in the Cu-MOF and negatively charged gap endowed by the -SO groups both act as ion sieve to facilitate the passage of Li and restrict the migration of polysulfide anions, synergistically mitigating the dendritic Li growth and polysulfides shuttling. As a result, the symmetric cell with MOF/Nafion separator achieves ultralong cycling stability (1000 h) and ultralow overpotential of 20 mV at a current density of 1.0 mA cm. Importantly, in the assembled Li-S full battery, the modified PP separator presents the superior cycle stability with capacity retention of 90% after 300 cycles at 0.5 C. Current outcomes open up a new route to design functional separators with ion permselective for realizing the dendrite-free and high-performance Li-S battery.