锂硫电池中醚类电解液的分解机理研究与体系优化

Lithium-sulfur (Li-S) batteries are one of the most promising candidates for next-generation rechargeable batteries. During the past decade, although substantial progress has been made and high capacity and long cycle life have been achieved by many groups, the practical application of Li-S batteries is still a formidable challenge. The most recent research found that the decomposition and depletion of ether-base electrolyte are largely responsible for the failure of the cell with ultrahigh sulfur loading, which is also the biggest barrier to the commercialization of Li-S batteries. To reveal the mechanism for the decomposition of ether-base electrolyte, we propose the use of in-situ techniques to study the decomposition process of ether-base electrolyte during the electrochemical discharging/charging, investigate their decomposition products and the formation of the SEI film on lithium metal anode. Then, we will try to find a solution to restrain the decomposition of ether-base electrolyte and the formation of stable SEI film on the lithium metal anode, so that the amount of electrolyte used in Li-S batteries could be reduced and the cycling performances of high energy density Li-S batteries could be improved. This project is expected to exert a positive effect on the establishment of the theoretical and technological foundation for the development of electrochemical stable electrolyte and promote the commercialization of Li-S batteries.

锂硫电池是最有前景的下一代高比能二次电池之一。虽然现在越来越多的研究小组都能在实验室中制备出高比容量和长循环寿命的锂硫电池，但是锂硫电池真正的商业应用却依旧缺鲜有耳闻。最近的研究表明，醚类电解液体系在电化学过程中的不断分解，耗尽直接导致了高容量锂硫电池的过早失效，是制约锂硫电池商业化推广的主要原因之一。本项目拟以揭示醚类电解液分解机制这一关键科学问题为契机，通过一系列原位表征测试手段，研究醚类电解液在电化学过程中的分解过程、分解产物以及在其分解过程在锂负极表面形成SEI膜的组成与机理。并在此基础上，对目前的醚类电解液体系进行优化，找到抑制醚类电解液分解与稳定金属锂负极SEI膜的有效方法，进而降低锂硫电池中电解液的用量，提高高比能锂硫电池的循环稳定性。项目的实施将为开发与设计电化学稳定的锂硫电池电解液体系提供科学依据与理论指导，为发展长寿命、高比能锂硫电池铺平道路。

锂硫电池具有低成本、高理论能量密度和环境友好等优点，被认为是最有前景的下一代可充电电池。醚基电解质具有高离子电导率、与锂负极良好的相容性、溶解中间体和降低反应势垒的能力，一直是锂硫电池最受欢迎的电解质。然而，基于醚-电解质的Li-S电池在低电解质与硫（E/S）比的情况下总是表现出较差的电化学性能。本项目中，我们证明了在低 E/S 比条件下，由于可溶性多硫化物的积累，醚基电解质在电化学过程中显着降低了电解质的润湿性和电导率，这增加了内部接触和电荷转移电阻，从而终止硫和硫化锂之间的转化，这是锂硫电池在醚类电解液中失效的根本原因。此外，我们还发现了抑制中间体溶解的新电解质来可以克服这些挑战。使用新配方的电解质，我们成功地改善了低 E/S 比下锂硫电池的电化学性能。当这种电解液用于锂硒电池时，我们发现了锂硒电池的新反应途径，即使使用高密度硒正极也能实现低反应势垒。此外，我们还提出了几种稳定锂金属负极的方法。我们的研究结果对奠定电化学稳定电解质开发的理论和技术基础，促进锂硫电池的商业化具有积极的作用。