功能化分级多孔碳的原位自活化制备与固硫机制研究

Owing to their high theoretical energy densities, lithium-sulfur batteries have been the next-generation high-efficiency energy storage devices, which hold huge potential applications in the field of smart grids and electric vehicles. However, their practical applications still face some insurmountable obstacles, for example, low utilization of active materials, poor rate performance, low coulombic efficiency, and short cyclic life. Based on the research status and trends in carbon-based materials for lithium-sulfur batteries, this proposal focuses on rational design and fabrication of functionalized hierarchically porous carbon (FHPC) hosts through molecular design. In contrast to the conventional chemical activation and template approaches, we aim to develop in situ self-activation for producing FHPCs so that to avoid the use of corrosive or toxic chemicals, and the troublesome and time-consuming post-processing. With the aim of obtaining high-efficiency and good stability cathodes, multiscale FHPC/sulfur composites that capable of solving the challenges of low sulfur loading and polysulfides shuttle will also be constructed. Meanwhile, we will try to clarify the interactions between the polarized carbon surface, hierarchical pores and the sulfur species using theoretical calculations and in situ monitoring techniques. Correspondingly, the synergistic effects and mechanisms for achieving superior electrochemical performance will be revealed, which would be advantageous for the industrialization of low-cost, high-performance lithium-sulfur batteries.

锂硫电池因具有高理论能量密度而有望成为继锂离子电池之后的新一代高效储能器件，在智能电网和电动汽车领域有着巨大的应用前景。然而，其实际应用仍面临着活性材料利用率低、倍率性能差、库仑效率低以及循环寿命短等难以逾越的障碍。本项目基于碳基材料在锂硫电池应用中的研究现状和发展趋势，提出从分子层面设计构建聚合物前驱体，发展原位自活化造孔技术，摒弃传统化学法和模板法造孔涉及强腐蚀或高毒性化学试剂、后处理过程繁琐耗时的弊端，实现功能化分级多孔碳基材料的可控制备。在此基础上，利用微纳加工技术构筑多尺度功能化分级多孔碳/硫复合材料，解决硫负载量低与多硫化锂穿梭的难题，获得高效、稳定的锂硫电池正极材料。并借助理论计算和原位探测技术阐明功能化碳材料极性表面、分级孔结构与含硫中间产物的微观作用过程，揭示其协同增效机制，推动低成本、高性能锂硫电池的产业化进程。

针对锂硫电池正极材料利用率低、倍率性能差、库伦效率低以及循环寿命短等问题，本项目通过引入功能化分级多孔碳主体材料，构筑了系列碳基复合电极，有效抑制了中间产物多硫化锂的扩散，显著提高了锂硫电池的电化学性能。发展了功能化多孔碳的原位自活化造孔技术，实现了新型碳基材料的简易、可控、规模化制备。通过构建微孔-介孔-大孔相互连通的开放性孔结构、杂原子掺杂、碳包覆/桥联过渡金属化合物复合结构，实现了对多硫化锂的限域和捕获，促进了离子/电子的传输，从而加速了其氧化还原转化动力学，获得了长循环寿命、高倍率性能锂硫电池。并利用原位电化学阻抗测试，首次实现了锂硫电池全过程的动力学定量分析，揭示了S8形成和Li2S沉积分别为电池充/放电过程的决速步，为高性能电极材料的理性设计提供了理论依据。在本项目的资助下，相关研究成果在Advanced Materials、Nano Letter、Research、Nano Energy等权威期刊上发表论文14篇，申请国家发明专利11项（已授权2项），在国内外重要学术会议上做主题/邀请报告7次，获陕西高等学校科学技术研究优秀成果一等奖，圆满完成了项目目标。

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