Fast redox conversion and low shuttle effect enabled by functionalized zeolite for high-performance lithium–sulfur batteries.

• A metallic cobalt-doped ZSM-5 zeolite with extra-framework Li+ is innovatively constructed. • The functionalized zeolite-modified separator endows lithium–sulfur batteries with fast redox conversion and low shuttle effect. • Superior cyclic stability, excellent rate capability, and negligible self-discharge behavior are achieved. Lithium–sulfur (Li–S) batteries are among the most promising next-generation rechargeable battery systems because of their high theoretical energy density and low cost. Nevertheless, the notorious shuttle effect of polysulfides and poor redox kinetics significantly limit their practical applications. Herein, a metallic cobalt-doped ZSM-5 zeolite with extra-framework Li+ is constructed to inhibit the migration of polysulfides and simultaneously enhance their conversion kinetics via a separator coating strategy. The ZSM-5 zeolite possessing a sub-nanometer channel structure acts as an ionic sieve, and effectively suppresses the undesired polysulfide migration by spatial constraint. The negatively charged zeolite framework with Li+ as counterions helps to facilitate the fast Li+ transport. More importantly, Co dopants further strengthen the interaction with polysulfides and work as active sites to improve the kinetics of sulfur redox reactions, which is verified by theoretical calculations and experiments. As expected, a Li–S battery employing the modified separator delivers superior long-term cyclic stability (only 0.04% capacity decay per cycle over 500 cycles at 1.0 C) and excellent rate capability (706 mAh g−1 at 3.0 C). In addition, the stable operation of an assembled Li–S pouch cell under various bending angles demonstrates its feasibility in practical applications. This work offers a new insight into the design of advanced separator modifiers for high-performance Li–S batteries. [ABSTRACT FROM AUTHOR]