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.依托材料创新塑造能源未来的背景下，锂硫电池（Lithium–Sulfur Batteries, LSBs）凭借极高的理论能量密度、比容量以及低廉的材料成本，成为顶尖级储能系统。尽管具备上述优势，锂硫电池仍存在可溶性多硫化物氧化还原物种向负极发生穿梭的问题，进而导致容量快速衰减与循环稳定性较差。除此之外，多硫化物的绝缘特性还会引发反应动力学迟滞，进一步加剧了这一隐患。为应对上述挑战，本研究通过将共价有机框架@石墨烯（Covalent Organic Framework@Graphene, COF@G）复合材料负载于电池隔膜，制备得到优化后的多硫化物阻挡兼转化催化剂。本研究选用结晶态TAPP-ETTB共价有机框架，因其具备富氮骨架与规则孔道结构，可为多硫化物提供充足的亲锂位点，实现对多硫化物的强化学吸附与催化作用。另一方面，石墨烯具备优异的电子迁移率，可加速硫氧化还原反应的动力学过程。因此，搭载TAPP-ETTB COF@G复合隔膜的锂硫电池表现出优异的电化学性能：首圈后在0.2 A g–1电流密度下可逆容量达1489.8 mA h g–1，循环400圈后仍保有920 mA h g–1的容量，且具备出色的倍率性能（2 A g–1电流密度下容量达827.7 mA h g–1）。在结晶态有机材料中利用其可设计性与合成结构调控手段的研究方向，是可持续材料、储能技术与锂硫化学交叉领域极具前景的研究范畴。