锂-硫电池用离子液体电解液研究

Due to their high specific energy, low cost and environmental-friendly character, Li-S batteries are promising candidates for electric vehicles. However, the Li-S batteries suffers from low capacity, poor cycling performance and safety issues due to the high solubility of the lithium polysulfides in the commonly used flammable ether-type electrolytes. Ionic liquid-based electrolytes have been considered as appealing candidates for Li-S batteries, as they can improve the electrochemical performance and the safety of the Li-S batteries due to their effectively suppressing the dissolution of the lithium polysulfides and non-volatile characteristic. Starting from the viewpoint of molecular structure design, the binding energy between the ionic liquids and the lithium polysulfides will be calculated by density-functional theory (DFT) calculation and suitable ionic liquids will be selected. The essence of the ionic structure on the electrochemical performance of the Li-S batteries will be investigated by using the state-of-the-art chemical and electrochemical characterization methods. This project intends to study the competition mechanism between the electrode and electrolyte with polysulfides, establish a reliable pathway to study the Li-S electrolyte by combining theoretical calculations and the experimental method in order to clarify the designing principles for Li-S battery electrolytes, not only enriching the theory of electrolytes, but also providing new ideas and theoretical basis for Li-S electrolyte.

锂-硫电池因其高比能、低成本、对环境友好等优点在电动汽车等领域极具应用潜力。然而，锂-硫电池目前使用易燃、易挥发的醚类有机电解液对中间产物多硫化物具有较高的溶解度，造成锂-硫电池循环性差并且存在严重的安全隐患。离子液体电解液因其可以有效抑制多硫化锂溶出及自身不挥发的特性在锂-硫电池中极具发展潜力。本项目从分子结构设计出发，采用密度泛函理论计算不同结构的离子液体与多硫化锂之间的相互作用，对离子液体进行理论筛选。在此基础上，利用先进的化学和电化学手段揭示不同离子结构对锂-硫电池电化学性能影响的本质。探索电极、电解液与多硫化锂相互作用的竞争机制，发展一种基于理论计算与实验相结合研究锂-硫电池电解液的新方法，阐明锂-硫电池电解液的设计原则，以丰富电解质溶液理论，为锂-硫电池电解液的科学设计提供新的思路和理论依据。

在项目执行的三年期间,围绕锂硫电池中电解液存在的问题展开。首先通过量子化学计算的方法,通过计算不同离子液体与多硫化锂之间结合能的大小，与氧化石墨进行对比，筛选出合适的离子液体体系P13TFSI。并将筛选出的离子液体与聚合物PEO进行复合制备得到离子液体基复合电解质用于常规锂离子电池和锂硫电池中.通过理论计算和实验相结合的方法，探究了电化学储能器件电解液的选择原则，为电解液的制备及研发提供了思路。