Ion-Selective Covalent Organic Framework Membranes as a Catalytic Polysulfide Trap to Arrest the Redox Shuttle Effect in Lithium-Sulfur Batteries.

Abstract

In the wake of shaping the energy future through materials innovation, lithium-sulfur batteries (LSBs) are top-of-the-line energy storage system attributed to their high theoretical energy density and specific capacity inclusive of low material costs. Despite their strengths, LSBs suffer from the cross-over of soluble polysulfide redox species to the anode, entailing fast capacity fading and inferior cycling stability. Adding to the concern, the insulating character of polysulfides lends to sluggish reaction kinetics. To address these challenges, we construct optimized polysulfide blockers-cum-conversion catalysts by accommodating the battery separator with covalent organic framework@Graphene (COF@G) composites. We settle on a crystalline TAPP-ETTB COF in the interest of its nitrogen-enriched scaffold with a regular pore geometry, providing ample lithiophilic sites for strong chemisorption and catalytic effect to polysulfides. On another front, graphene enables high electron mobility, boosting the sulfur redox kinetics. Consequently, a lithium-sulfur battery with a TAPP-ETTB COF@G-based separator demonstrates a high reversible capacity of 1489.8 mA h g-1 at 0.2 A g-1 after the first cycle and good cyclic performance (920 mA h g-1 after 400 cycles) together with excellent rate performance (827.7 mA h g-1 at 2 A g-1). The scope and opportunities to harness the designability and synthetic structural control in crystalline organic materials is a promising domain at the interface of sustainable materials, energy storage, and Li-S chemistry.