硫正极聚硫阴离子微区束缚结构的构筑及电化学性能研究

The shuttle effect of polysulfide anions is an important factor of influencing cycle performance for lithium-sulfur batteries. The results of restraining polysulfide anionic shuttle are unsatisfactory by physical adsorption of porous carbon materials, and the interaction of physical adsorption is obviously smaller than that of chemical adsorption. Additionally, a unique microenvironment from the binder around the active material is formed, in which an effective chemical adsorption to polysulfide anions is desired through the functionalization of binders with reactive groups. For the present project, the switching molecules, such as spiropyrans or oxazines, with the recognition to nucleophilic anions will be introduced to functionalize adhesives. With the purpose of reducing shuttle effect, a polysulfide anionic micro-area restrained structure will be possibly explored on the base of improved binder, and the structure would prevent polysulfides from dissolving and migrating to the electrolyte through the reversible chemical adsorption of soluble polysulfide anions with the reversible nucleophilic addition reaction. With insight to full electrochemical characterization of sulfur cathodes prepared by functionalized binder, the structure-activity relationship will be discussed and revealed between the electrochemical behaviors and the switching molecular structure and “on/off” state. This project will provide a new research idea for reducing the shuttle effect, and is also beneficial to improve cycle performance of lithium-sulfur battery.

聚硫阴离子的穿梭效应是影响锂硫电池循环性能的一个重要因素。依靠多孔碳材料的物理吸附来抑制穿梭效应的效果有限，并且物理吸附作用力明显小于化学吸附作用力。围绕在活性物质周围的粘结剂构筑出独特的微区环境，利用其分子中含有的活性基团进行功能化有望对聚硫阴离子形成有效的化学吸附。本项目拟采用对亲核性阴离子具有识别功能的螺吡喃或噁嗪类开关分子进行粘结剂功能化，构筑聚硫阴离子的微区束缚结构。通过可逆亲核加成作用实现聚硫阴离子的可逆化学吸附，阻止其向电解质的溶解和迁移，降低穿梭效应。借助正极电化学性能的充分表征，揭示开关分子的分子结构、“开/关”状态与电化学性能之间的构效关系。本项目的开展将为降低聚硫阴离子的穿梭效应及提高锂硫电池循环性能提供新的研究思路和科学依据。

影响锂硫电池循环性能的一个重要因素是聚硫阴离子的穿梭效应。目前主要依靠多孔碳材料的物理吸附和功能隔膜来抑制穿梭效应的作用效果有限，并且物理吸附的作用力明显小于化学吸附。围绕在活性物质周围的粘结剂构筑出独特的微环境，利用其分子中含有的反应基团进行功能化有望对聚硫阴离子形成有效的化学吸附。.首先，以水为溶剂的海藻酸钠粘结剂用于锂硫电池硫正极的制备进行研究。 EIS测试结果表明水溶性Ca2+-Alg基硫正极比以N-甲基吡咯烷酮（NMP）为溶剂的聚偏氟乙烯（PVDF）基硫正极阻抗小，动力学性能更好。充放电测试结果表明以Ca2+-Alg为粘结剂的硫正极在0.5C电流密度下循环200圈放电容量为383 mAh g-1，容量保持率为80.5%，比起PVDF基硫正极有更好的循环稳定性能。这些结果表明，Ca2+-Alg是有前途的应用于锂硫电池的粘结剂。.其次，制备了一种小分子凝胶电解质材料，初步探索了有机小分子凝胶作为锂硫电池电解质材料的可能性。制备的小分子凝胶电解质在常温下具有6.43×10-3 S cm-1的离子电导率，用其制备的一次锂硫电池正极的放电容量也有1008 mAh g-1（0.1 C）。.最后，利用聚酰胺酸与多巴胺之间反应制备了新型功能粘结剂（PAA-DA）。PAA-DA分子链上的酰胺基、亚胺基等可以与多硫化锂形成类化学键作用，降低多硫化锂的溶解穿梭，提高电池的循环性能。实验结果表明：在1 C电流密度下，PAA-DA电极首圈为720 mAh g-1，循环100圈后，容量保持550 mAh g-1；高于PVDF正极的容量320 mAh g-1。.本项目的开展将为利用化学吸附降低聚硫阴离子的穿梭效应提供新的研究思路，并为提高锂硫电池正极循环性能的研究提供新途径。