A sandwich-structured bifunctional separator for durable and stable lithium-sulfur batteries

The shuttle effect of polysulfide (PS) and dendrite growth are two main obstacles in the development of lithium-sulfur (Li-S) batteries. Herein, we propose a sandwich-structured metal–organic framework (MOF)-based separator with UiO-66-(OH)2 membranes symmetrically prepared on polypropylene separator for these challenges. On one aspect, the UiO-66-(OH)2 membrane can selectively block PS through the size sieving and electrostatic repulsion effect towards the neutral PS molecules and negatively charged PS ions, respectively. In addition, the reaction kinetics are also promoted by the introduced MOF membrane. On the other aspect, with lipophilic groups and ordered channels, this MOF membrane facilitates a rapid and uniform Li+ diffusion, thereby suppressing the Li dendrites. Consequently, Li-S batteries with this double-side modified separator exhibit a surprising capacity of 903 mAh g−1 and a long cycling stability with a low decay of 0.046% per cycle for 600 cycles under 2C. Even at raised sulfur loading and lean electrolyte conditions, exceptional cycling and rate performance can be still achieved. This work will advance the construction of multifunctional nanomaterials for Li-S batteries.