基于小分子硫原位还原氧化石墨构建的嵌层结构锂-硫电池正极材料及其性能研究

Lithium-sulfur (Li-S) batteries are still plagued by low active material utilization and poor cycle life, arising mainly from insulating nature of sulfur, dissolution of high-order lithium polysulfide intermediates (Li2Sx, 4≤x≤8) in liquid electrolytes, dissolved lithium polysulfides shuttle between anode and cathode, and large volume change during lithiation/delithiation. Extensive researches have been conducted to overcome these challenges. Among them, one of the most attractive strategies is to encapsulate S with self-supporting and void-containing carbon matrix. On basis of our recent related studies, the present project starts from the construction of novel intercalated small molecular sulfur in the interlayer of reduced graphite oxide (RGO) composite as a stable Li-S battery cathode via in-situ one-step sulfur reduction and intercalation of graphite oxide strategy. Firstly, the fabrication condition and ruler of the small molecular S intercalated in the interlayer of RGO, upon which the critical factors that affect the construction of the stable S intercalated reduced graphite oxide (RGO/S) cathodes for Li-S battery will be revealed. Secondly, the efficacy of RGO/S fabrication on the improvement of electrochemical properties in Li-S batteries will be ascertained based on the systematical investigation of structural and electrochemical properties of the RGO/S composite. The third task of this project is to explore the interaction and microstructure evolvement of components during cycling, and to clarify the the mechanism of electrochemical property improvement of the RGO/S cathode in Li-S batteries. In one word, the implementation of this project will provide the relaible theoretical basis and technical guidance for the optimization design and electrochemical performance improvement of C/S composite cathodes and other S-based composite cathodes in Li-S batteries.

锂-硫电池因正极材料硫导电性差、放电时体积膨胀以及生成的多硫化物易溶于电解液等，结果导致活性物质利用率低和循环性能差，而采用碳材料作为硫的导电网络和弹性支撑体来构建碳/硫复合电极材料体系是改善锂-硫电池电化学性能的重要途径。在前期工作的基础上，本项目拟以氧化石墨为先驱体，在硫高温原位还原氧化石墨过程中形成的膨胀石墨/小分子硫嵌层结构锂-硫电池正极材料体系的构建为出发点，研究高稳定膨胀石墨/小分子硫复合电极材料的形成规律和条件，揭示影响嵌层结构膨胀石墨/小分子硫复合电极材料体系构建的关键因素；系统分析电极材料在锂-硫电池中的电化学性能；探索体系中碳与硫组元在充/放电过程中的微观化学和物理性质，从根本上阐明硫基电极材料电化学性能改善的微观机制。通过这些研究，为碳/硫复合电极材料和其他硫基复合电极材料的优化设计和综合电化学性能的改善提供理论依据和技术支持。

提高硫的导电性和消除溶解的多硫化物的“穿梭效应”是实现高性能锂-硫电池的关键，而稳定化的小分子硫S2负载在三维碳基载体有望能够实现锂-硫电池正极材料电化学性能的提升。项目通过硫高温原位还原氧化石墨制备稳定膨胀石墨/小分子硫嵌层结构的硫基正极材料，结果表明活性物质硫均匀地分布在石墨层间，且该膨胀石墨/硫复合电极材料在保持高活性硫载量下具有较好的循环稳定性能，并深化认识了膨胀氧化石墨的氧化程度跟硫载量和电池循环稳定性的关系和影响机制；针对锂-硫电池存在“穿梭效应”的难题，构建荷电高分子/碳基材料等修饰的导电型、双功能复合隔膜，利用“化学静电作用”和物理吸附稳定多硫化物，协同提升锂-硫电池循环稳定性；并基于协同稳定作用，利用静电纺丝等技术制备纳米金属和富氮掺杂的三维导电碳基锂-硫正极材料进一步提升锂-硫电池的综合性能，实现了在高硫担载量下（80 wt%）较高的初始比容量（~1064 mAh g-1）、长循环稳定性和优异倍率性能。这些将为设计和开发高性能的储能电池电极材料奠定了坚实的基础。基于本项目的资助，已发表SCI论文16篇；申请专利17项，含授权专利4项；已培养博士1名、硕士3 名；另获项目资助3项。