MOF and related composites as selective functional separators and interlayers for Li-S batteries

Lithium-sulfur (Li-S) batteries are one of the most promising technologies compared to the Li-ion based ones, mainly due to their outstanding high energy density (2567 Wh/kg). Nonetheless, Li-S batteries still face important drawbacks, namely the shuttle effect caused by the polysulfides dissolution into the electrolyte and their escape from the cathode, leading to active material loss and ultimately to the anode passivation. Mitigating this effect is crucial to boost the Li-S technologies at large scale and the rational design of the separator or interlayer is considered as an effective solution. Metal-Organic Frameworks (MOFs) and related composites have been recently proposed as candidates to selectively capture the polysulfides, due to their tunable structures and compositions and ordered micro- or meso-porosity which can sieve polysulfides through physical barriers or chemical sorption as well as catalyze polysulfide conversion kinetics. Moreover, once introduced into composites membranes as functional separators and interlayers, this promote their easy inclusion in Li-S devices. This short review summarizes the recent progresses in this field, emphasizing the different types of functional separators and interlayers integrating MOFs and proposes new research directions to optimize these systems.