调控电催化剂电子结构促进锂硫电池多硫化物催化转化的研究进展

Recent progress in electronic modulation of electrocatalysts for high-efficient polysulfide conversion of Li-S batteries

锂硫电池具有高的理论能量密度(2600 Wh kg^(-1)),是传统金属氧化物正极和石墨负极组装的锂离子电池能量密度的3-5倍.同时,锂硫电池以单质硫作为活性物质,具有环境友好及价格低廉的优势,因此被认为是最具发展前景的电化学储能系统之一.然而,锂硫电池的商业化应用仍面临诸多挑战和障碍,比如单质硫和放电产物硫化锂的绝缘特性,活性物质充放电过程中的体积变化以及多硫化物穿梭导致的活性物质不可逆损失、低的库伦效率及差的循环稳定性等.对于单质硫及放电产物的绝缘特性,可通过构建高导电的网络结构或者减小硫颗粒尺寸来克服.对于充放电过程中活性物质的体积变化问题,可通过制备柔性电极或者设计具有分级多孔的三维网络结构材料来克服.唯独对多硫化物的穿梭问题,还没有找到一种方案来有效解决.锂硫电池前期的研究工作主要通过调控载体材料的物理结构实现对多硫化物的物理及化学吸附,从而在一定程度上抑制了多硫化物的穿梭.然而多硫化物穿梭的产生不仅仅与多硫化物的迁移扩散有关,更与载体材料界面处多硫化物迟缓的氧化还原转化有关.当载体材料界面处多硫化物无法实现快速转化时就会导致界面处多硫化物的富集,进而导致严重的穿梭效应.因此,引入各类电催化材料来加速多硫化物的氧化还原转化被认为是更有效抑制穿梭效应的策略之一.目前已报道的锂硫电池综述大多侧重从催化材料本身的物理及化学结构特性出发进行归纳总结,但是对于催化材料本身的电子结构与催化活性间的关系鲜有探讨.实际上,电催化剂的电子结构在改善催化剂的催化活性进而加速多硫化物氧化还原转化方面起着决定性作用,因此合理调控电催化剂的电子结构对于抑制穿梭效应,进而提高锂硫电池的电化学性能具有至关重要的意义.本文全面概述了锂硫电池中电催化剂电子结构的调控策略,包括但不限于空位工程、杂原子掺杂、单原子掺杂、能带调节、合金化及异质结构工程等.此外,分析了设计高效电催化剂,构建高能量密度和长寿命锂硫电池的未来发展前景和面临的挑战.

With the merits of high energy density,environmental friendliness,and cost effectiveness,lithium-sulfur(Li-S)batteries are considered as one of the most promising next-generation electrochemical storage systems.However,the notorious polysulfide shuttle effect,which results in low active material utilization and serious capacity fading,severely impedes the practical application of Li-S batteries.Utilizing various electrocatalysts to improve the polysulfide redox kinetics has recently emerged as a promising strategy to address the shuttle effect.Specially,the electronic structure of the electrocatalysts plays a decisive role in determining the catalytic activity to facilitate the polysulfide conversion.Therefore,reasonably modulating the electronic structure of electrocatalysts is of paramount significance for improving the electrochemical performance of Li-S batteries.Herein,a comprehensive overview of the fascinating strategies to tailor the electronic structure of electrocatalysts for Li-S batteries is presented,including but not limited to vacancy engineering,heteroatom doping,single atom doping,band regulation,alloying,and heterostructure engineering.The future perspectives and challenges are also proposed for designing high-efficient electrocatalysts to construct high-energy-density and long-lifetime Li-S batteries.