基于天然植物纤维制备锂硫电池用新型多孔碳

Lithium sulfur batteries（LSBs） have attracted researchers extensive attention because of a high theoretical energy density, low cost and environmentally benign characteristics. Despite these significant advantages, there are several problems and challenges that have to be solved for LSBs, such as the low electron conductivity of sulfur, the dissolution and diffusion of polysulfide intermediates, and the volume expansion and shrinkage of sulfur intermediates during cycling. Conductive carbon materials such as porous carbons, carbon nanotubes and graphene can act as a suitable host matrix encapsulating sulfur to improve the performance of sulfur cathode. However, the sophisticated preparation process, the difficulty of high production, the use of exotic templates and/or costly surfactants, and high-cost carbon sources restricted their large-scale applications. Hence, carbon materials derived from low-cost renewable natural plant fiber with appropriate physical properties and chemical components would probably be an ideal candidate for LSBs. In this project, we use cyclosorus interruptus and palm fibe as carbon sources to prepare porous carbon (PC) for LSBs. According to our previous work, the PC possess a microporous wall and inner tube array, PC/S composites showed outstanding performance as cathodes in LSBs, the initial specific capacity near to 1300 mAh g-1, the specific capacity around 700 mAh g-1 after 100 cycles, the coulombic efficiency up to 100%. In this project, we will study the mechanism during carbonization of natural plant fiber, dope the PC to improve the electrochemical performances of sulfur electrode, explore the methods to prepare the PC/S composites, provide more theory and technology principle for the commercial application of LSBs.

锂硫电池因具有能量密度高、价格低廉和环境友好等特点而得到广泛关注。锂硫电池存在单质硫导电性差、中间产物多硫化物的溶解以及中间产物在充放电过程中的体积膨胀和收缩等问题。多孔碳、碳纳米管和石墨烯等碳材料负载硫可以提高硫电极的性能。但碳材料的合成过程复杂、难于量化生产、使用昂贵的模板剂和表面活性剂以及碳源成本高等问题制约了锂硫电池的大规模应用。因此，采用廉价、可再生的天然植物纤维制备锂硫电池用碳材料是一个理想的选择。本项目中，我们采用毛蕨和棕榈纤维为碳源制备锂硫电池用多孔碳。前期研究结果显示：所得多孔碳具有微管阵列结构，碳/硫复合材料具有较好的电化学性能，首次放电比容量接近1300mAh.g-1，循环100次后放电比容量仍然有700mAh.g-1，充放电效率达100%。本项目中，我们主要进行植物纤维碳化机理研究；多孔碳掺杂改性研究；碳/锂复合材料制备方法探讨；为锂硫电池商业化提供理论和技术支持。

根据项目的研究目标和内容，我们主要从生物质炭化条件，活性炭的构效关系、碳材料结构调控，活性硫形态控制等方面开展了研究。获得了四种性能优异的锂硫电池载硫用活性炭；制备了载硫量高达92wt%的石墨烯包裹的菱形活性硫复合材料；可以7C倍率充放电的N,S共掺杂碳点石墨烯复合材料。在该项目经费的资助下，发表论文11篇，授权发明专利2项。完成项目的研究任务，达到预期效果。