离子液体与含氮多孔碳材料协同构建高能量密度锂硫电池

Lithium-sulfur (Li-S) batteries owing to their high theoretical energy density and low cost have been considered as one of the most promising next-generation batteries. However, their practical energy density is still much lower than expected at present, probably because of the inevitable use of a significantly excess amount of polysulfide-soluble ether electrolyte in most cases. This project intends to overcome this issue by using several aprotic and solvate ionic liquids as the typical polysulfide-insoluble electrolytes for Li-S batteries. Since these ionic liquids have weak Lewis acidity and basicity simultaneously, the dissolution of polysulfides and thus the severe “shuttle” effect occurred in ether electrolytes should be suppressed. Therefore, the amount of electrolyte volume relative to the sulfur mass (E/S, μL/mg) can be greatly reduced. In combination with the highly conductive N-doped porous carbon materials as the cathodic host, one can finally improve the practical energy density of Li-S batteries. This study will be carried out by the following procedures: First, the correlation between ionic liquids and carbon materials will be studied to get the best cathodic carbon supports for ionic liquid electrolytes. Then, the possible solid-state redox mechanism of the active materials will be investigated. Next, high-performance carbon/sulfur cathode will be fabricated by optimization of the C/S mass ratio and improvement of the area capacity of the cathode. Finally, Li-S batteries with both high practical energy density and long cycle life will be achieved by reduction of the electrolyte volume/sulfur mass ratio. This proposal may shed light on the in-depth investigation of other polysulfide-insoluble electrolytes such as concentrated solutions. It should also promote the development of highly efficient and clean energy including Li-S batteries.

锂硫电池因其高的理论能量密度和低的成本被认为是极具商业应用前景的新一代电池技术，但是目前其实际能量密度仍然很低，这主要是因为一般锂硫电池需要使用远超实际用量的能溶解多硫化物的常规醚类电解液。本项目拟采用同时具有弱Lewis酸性和碱性的非质子酸和溶剂化离子液体作为锂硫电池的电解液，并结合高导电性的含氮多孔碳正极载体，利用上述离子液体能极大抑制多硫化物溶解和“穿梭效应”的特性，大幅度降低电解液的用量，最终提升锂硫电池的实际能量密度。具体研究内容包括：考察离子液体电解液与碳材料载体之间的协同匹配性并探索活性物质可能的固相电化学反应机制；通过优化碳/硫质量比和提高面积比容量构筑高性能碳/硫复合正极；降低电解液与硫活性物质的体积/质量比，实现锂硫电池的高能量密度与稳定充放电循环。本项目的实施，对研究其它一般性不溶多硫化物的电解液、提高锂硫电池性能和发展清洁高效能源具有重要的科学意义和应用价值。

锂硫电池因具有高能量密度、高理论容量、单质硫资源丰富、价格低廉以及环境友好等特点成为新型高性能电池的主要研究方向之一。但是单质硫和放电产物硫化锂的低电导率、多硫化物穿梭效应、充放电过程中活性物质体积变化大等一系列问题，严重制约了其商业化应用。本项目针对上述系列问题，通过设计制备新型碳材料与离子液体功能材料，并将二者进行有机结合，构建了高性能锂硫电池。一是设计制备了包括具有极窄孔径分布的微孔碳、含氮微孔碳以及基于缺陷普鲁士蓝和碳纳米管的三维交互微复合结构在内的一系列碳基载体，构筑了高性能持碳/硫复合正极。二是通过分子水平设计和引入强的氢键作用，设计制备了一系列基于离子液体的新型粘附材料，其在多种基底表面表现出远高于商用粘结剂的粘附特性。将其中一种低成本聚离子液体作为水溶性粘结剂用于锂硫电池时，展现出比商品化粘结剂更优异的电池性能。三是采用理论模拟了锂硫电池中纳米限域的Li2S的反应机理。尽管整个脱锂过程是氧化反应，但可以观察到局部还原和歧化反应。Li2S作为活性材料的激活充电过程仅要0.37V的过电位。.项目的各项指标均已完成且完成情况良好。通过项目的顺利开展，构建了基于离子液体材料和多孔碳载体的锂硫电池体系，通过优化电解液和碳/硫复合正极等关键因素，有效抑制了锂硫电池中多硫化物“穿梭效应”的发生，掌握了小分子硫/硒在纳米限域状态下的电化学反应过程以及与作用机理，实现了锂硫电池的高比容量、稳定的充放电循环、较好的倍率性能。本项目的实施，对于进一步拓展离子液体功能材料在锂硫电池中的应用研究具有重要意义。.项目执行期间，在Advanced Materials，Journal of Materials Chemistry A，Small，Journal of Energy Chemistry，ACS Applied Materials & Interfaces，Physical Chemistry Chemical Physics等期刊上发表标注基金号的论文16篇，申请中国发明专利2件，授权1件，培养博士后1人（入选国家博新计划）、博士研究生2 名（在读2名），硕士研究生9名（在读5名，毕业4名）。