仿生催化MOF材料的正极硫载体的设计及其在锂硫电池中的应用研究

Sulfur Cathode Design Based on Bio-Catalytic Metal-Organic Framework and Its Catalytic Performance in Lithium-Sulfur Batteries

摘要:

锂硫电池（LSBs）以1 675 mAh?g^-1的高理论比容量和2 600 Wh?kg^-1的高理论能量密度，被视为未来储能体系的有力竞争者。然而，LSBs在充放电过程中所产生的穿梭效应，导致多硫化物（LiPSs）在电解液中溶解和正极活性物质损失，从而引发容量衰减，严重限制了其实际应用。因此，设计具有高效催化活性的材料，以限制LiPSs扩散并加速其氧化还原反应动力学，被认为是解决上述问题的关键途径。虽然生物小分子催化剂具有优异的氧化还原特性，但在传统电解液中的高溶解性却限制了其循环稳定性。以金属团簇作为中心和有机配体作为连接单元所组成的金属-有机框架材料（MOFs），具有比表面积大、孔隙率高、孔结构高度有序、结构可调和可设计性等优势，通过分子工程设计有望在其纳米空间中实现对有机小分子催化剂的固定和精确调控。为此，基于仿生催化理念，设计了一种新型MOF（UiO-TECP），即将生物还原剂三(2-羧乙基)膦（TCEP）通过纳米限域策略固定于MOF孔道内，制备高效硫载体材料。其中，MOFs的有序孔道结构通过纳米限域作用来抑制LiPSs的扩散，而孔内固定的TECP能够有效促进二硫键的断裂，加速LiPSs的转化反应。电化学测试结果表明，基于S/UiO-TECP正极的LSBs在1 C电流密度下实现了841.6 mAh?g^-1的初始放电比容量，并在500圈循环中保持极低的容量衰减率（每圈0.06%）。通过将仿生催化与MOF结构设计相结合，显著提升了LSBs的循环性能和动力学特性，为开发新型多功能硫载体材料提供了重要理论支撑与实践指导。

Abstract:

Lithium-sulfur batteries （LSBs） are promising candidates for next-generation energy storage systems due to their high theoretical specific capacity （1 675 mAh?g^-1） and energy density （2 600 Wh?kg^-1）. However， the solubility of long-chain lithium polysulfides （LiPSs） in the electrolyte during charging/discharging cycles lead to the shuttle effect， resulting in active material loss from the cathode and capacity degradation. Designing efficient and catalytically active materials to limit LiPSs diffusion and accelerate redox reaction kinetics is crucial to addressing these challenges. Small-molecule bio-catalysts exhibit excellent redox properties， making them ideal candidates. However， their high solubility in conventional LSBs electrolytes causes catalytic material loss during cycling. Metal-organic frameworks （MOFs）， featuring metal clusters and organic linkers， offer advantages such as high specific surface area， tunable pore structures， and structural versatility. By leveraging molecular engineering， small organic molecule catalysts immobilized and precisely regulated within the nanoscale confines of MOFs. Therefore， a biomimetic catalytic MOF catalyst （UiO-TECP） was developed using a nano-confinement strategy to immobilize the bio-catalytic unit TCEP within MOF pores， serving as an efficient sulfur host. The MOF’s ordered pore structure inhibits LiPS shuttle， while confined TECP accelerates disulfide bond cleavage， enabling rapid LiPSs conversion. The S/UiO-TECP cathode demonstrated a high initial discharge capacity of 841.6 mAh?g^-1 at 1 C and outstanding long cycle stability over 500 cycles， with a capacity decay rate of just 0.06% per cycle. The biomimetic design highlights a promising approach to overcoming LiPSs shuttle effects and offers a pathway for developing advanced catalytic hosts for high-performance LSBs.