基于“微胶囊”结构的锂硫电池正极材料设计、制备及性能研究

Low sulfur utilization and poor cycling stability are considered as the key problems for the application of lithium-sulfur (Li-S) batteries. Bearing these problems in mind, particular structured matrices embodied with e- conductive carbon wall for S/Li2S deposition and Li+ conductive window will be designed and then synthesized in this project. Several natural high molecular polymers and lithium sulfide are chosen as the sources of carbon microcapsule and sulfur core respectively. Based on the microcapsule structure, cathode materials with high sulfur dispersion, low sulfur loss and little expansion effect will be designed and synthesized. More specifically, in order to improve the utilization of sulfur, microcapsule wall is chosen as the carrier to disperse sulfur. Moreover, bi-functional microcapsule wall is used as the protective layer for trapping the polysulfides effectively; the gap between the microcapsule wall and the microcapsule core is employed for buffering the expansion stress, for avoiding the structural collapsing during charge and discharge process. This project is expected to provide alternative idea and methodology for excellent sulfur fixation and good cycling stability, and to promote the Li-S battery development in both scientific research and practical application aspects.

针对高比能锂硫电池正极材料存在的硫利用率低、循环稳定性差等问题，本项目拟从构建抑制多硫化物“穿梭效应”的物理屏障出发，以高分子材料为囊壁碳源、固态电解质为囊壁孔道锂离子导体、硫化锂为囊芯硫源，制备使活性物质满足“分散度高、溶解流失少、膨胀效应小”要求的“微胶囊”结构正极材料。采用胶囊壁内壁作为活性物质的载体，使其高度分散，提高利用率；利用具有离子传导、电子传导双功能特性的胶囊壁作为活性物质的保护壳，消除/抑制电解液传导锂离子带来的多硫化物溶解流失问题，充分发挥固硫效能；借助囊壁与囊芯间的空隙以缓解反应过程中硫电极的体积膨胀，避免充放电过程中囊壁碳材料的结构坍塌，保持电极的完整性。本项目的实施，将为锂硫电池实现活性物质的高效利用和有效固定提供新思路、开辟新途径，对推进锂硫电池的发展具有重要科学意义和实用价值。

锂硫(Li-S)电池凭其高理论比能量、低成本、环境友好等特点，被认为最有前途的下一代储能系统。研究表明，提高Li-S电池电化学性能的关键是获得能有效抑制多硫化锂穿梭效应的导电基体材料。基于此，本项目研究开发了能显著改善Li-S电池充放电比容量、倍率及循环稳定性的新型导电基体材料（碳复合过渡金属氧化物、硫化物、磷化物等），为Li-S电池的研究提供了可靠的实验数据和理论指导。取得的主要结果如下：.1）采用溶胶凝胶法制备了导电碳（SP）复合磷酸钛锂（LTP）的硫基体材料，基于LTP的高导电性，SP-LTP-S比SP-S放电比容量提升了200 mAh/g。.2）采用自模板法，借助柯肯达尔效应，制备了具有类“微胶囊”结构的NiCo2S4@C作为硫基体材料，因NiCo2S4的强极性、高导电性，加快了多硫化锂氧化还原反应动力学，缓解了穿梭效应，改善了电池的循环稳定性。.3）MIL-53衍生的Fe3O4@C作为硫基体材料，凭借Fe3O4对多硫化锂的强化学吸附作用，300次循环后容量保持率大于99 % (1.0 C)。.4）制备了以碳化物为囊芯，碳为囊壁的 “微胶囊”结构硫基体材料，5 C放电，比容量约800 mAh/g。. 上述结果表明，通过调控硫基体材料组分、形貌、结构等，可有效改善硫正极导电性，缓解穿梭效应，提高Li-S电池的电化学性能。.