面向致密锂硫电池的传导金属基纳米点/MXene高效催化剂构筑及机理研究

锂硫电池具有比目前商业化锂离子电池大约十倍的理论容量，是最有希望实现产业化的新一代高比能动力电池。但硫正极的多硫离子溶解和死硫及体积能量密度低一直是锂硫电池的研究和实际应用面临的难题之一，通过催化转化多硫离子是解决该难题的有效途径。本项目拟采用MXene来稳定催化效应的传导金属基纳米点（<5 nm）的新策略，再以少量石墨烯取代电极用的乙炔黑作为组装剂，制备高度致密的金属基纳米点-MXene硫复合电极材料，以实现高效的宿主催化剂固硫和正极材料的致密化。利用MXene高导电和能化学吸附多硫离子的特点，通过金属基纳米点催化剂高效转化多硫离子，从而抑制多硫离子的溶解和死硫现象，甚至实现无穿梭效应；利用致密硫电极具有的三维传导网络和高致密优势，实现高面硫载量和锂离子的致密储存。研究MXene稳定金属基纳米点催化剂及协同固硫和催化机制以及致密储能机理，为高体积能量密度的锂硫电池提供理论指导。

Lithium-sulfur batteries (LSBs) are very promising for the next-generation high-energy-density rechargeable batteries, because of their high theoretical specific capacity with about ten times as high as that of commercial lithium-ion batteries. However, sulfur cathodes of LSBs are facing several serious issues including the dissolution of polysulfides, the phenomenon of “dead sulfur”, and low volumetric energy density, which is also the one of critical challenges in the scientific research and practical application for LSBs. Catalyzing the conversion of polysulfides is an effective strategy to solve the above-mentioned issues in sulfur cathodes. In this project, we will explore an efficient strategy to prepare novel metal-based nanodots/MXene hybrids by using MXene to stabilize conductive metal-based nanodots (Diameter < 5 nm), which serve as sulfur immobilizers and high-efficient catalysts in sulfur cathodes. And then, a small amount of graphene (≤12 wt%) as conductive additive (instead of acetylene black) and simultaneously as “assembled binder” was employed to further densified the as-prepared sulfur cathode, thus designing highly dense metal-based nanodots/MXene sulfur cathodes. By taking the advantages of high conductivity and strong anchoring of polysulfides for MXene, and combining with such characteristics of conductive metal-based nanodots such as high-efficient catalytic ability for the conversion of polysulfides, the highly dense metal-based nanodots/MXene sulfur cathodes can efficiently confine the polysulfides and catalyze the conversion of polysulfides, thus to suppress the dissolution of polysulfides and avoid the phenomenon of “dead sulfur” during cycling, even to achieve the shuttling-free LSBs. Besides, we take advantage of three-dimensional conductive network and highly dense structures of sulfur electrodes to achieve the high area loading of sulfur and the compact lithium storage. Through investigating the mechanism of stabilization of metal-based nanodots by MXene and the densification of sulfur electrodes, elucidating the synergistic effect between MXene and metal-based nanodots for the synchronous immobilization and conversion of polysulfides, and revealing the mechanism of compact energy storage, it will provide the theoretical guidance for LSBs with high volumetric energy density.