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

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.