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 lithium-ion-based ones, mainly due to their outstanding high energy density (2,567 Wh/kg). Nonetheless, Li-S batteries still face important drawbacks, namely the shuttle effect caused by the polysulfide 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 a large scale and the rational design of the separator or interlayer is considered as an effective solution. Metal-Organic Frameworks 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 and catalyze polysulfide conversion kinetics. Moreover, once introduced into composite membranes as functional separators and interlayers, this promotes their easy inclusion in Li-S devices. This short review summarizes the recent progress in this field, emphasizing the different types of functional separators and interlayers integrating Metal-Organic Frameworks, and proposes new research directions to optimize these systems.