共生型多孔石墨化炭/氮化硼复合载体制备及在锂硫电池正极中的应用

Lithium-sulfur battery is currently one of the most promising secondary batteries. However, the commercialization of Li-S battery is inhibited by serious capacity fading caused by the insulating nature of sulfur, volume expansion, high solubility of lithium polysulfides in electrolytes during charge/discharge proccess. Rational design of the cathode materials is key to fundamentally solve the problem of lithium-sulfur batteries. Considering the combination of the electroconductive, porous and graphitized properties of carbon materials and the light weight, easily adjustable polarity and 2D structure properties of boron nitride, this project aims to investigate on the function-oriented design of carbon/boron nitride paragenesis composites with enhanced conductivity, high porosity and strong polarity. We will clarify the cooperative regulation mechanism of the pore structure, polarity, conductivity, and catalytically active sites in stabilizing the sulfur species through the synergetic triple action of physical adsorption, chemical adsorption and catalytic conversion. The microstructure evolution of the sulfur cathode and the dissolution behavior of polysulfides during the charge/discharge process were investigated using various characterization methods and theoretical calculation. More importantly, the mechanism of interaction between sulfur species and the interfaces of such paragenesis composites will be figured out at the molecular level. Thus, we tend to understand the structure functions (e.g, conductivity, porosity, polarity, etc.) corresponding to the cycle stability and self-discharge behavior of the lithium-sulfur batteries. This study would provide theoretical and experimental basis for further development of a new type of high safety and high performance lithium sulfur batteries system.

锂硫电池极具应用前景，但硫单质不导电、多硫化锂溶解迁移等问题导致锂硫电池稳定性难以满足应用需求。合理设计硫正极材料结构是从源头解决以上问题的有效途径。本项目提出利用炭材料导电、多孔、易石墨化的性质和氮化硼轻质、极性易调、二维层状结构的特点，借鉴“共生”概念，通过合成策略创新，构建无缝连接共生型高导电、高孔隙、强极性石墨化炭/氮化硼复合材料，揭示其孔结构、极性、导电性、表面活性位的协同调控规律；借助物理吸附、化学吸附、催化转化三重作用，协同增效，实现硫物种的高效固载和利用，采用谱学表征结合理论计算，定量分析材料的固硫作用和多硫化锂的溶出行为，在分子水平理解硫物种与载体材料表/界面的相互作用机制，获得材料的导电性、孔隙率、极性等与电池循环稳定性、自放电行为之间的关联规律。解决单质硫作为电极材料稳定性差的问题，提高硫的利用率，建立炭/氮化硼载硫新体系，为构建新型高性能锂硫电池提供指导。

本项目立足合成策略创新，从分子角度设计出发，制备出不同孔隙率以及形貌的炭材料，发展了纳米定制炭材料结构的新方法。通过自催化辅助的自下而上方法调控炭材料的石墨化程度，提升材料的导电性；进一步将具有强极性的杂原子掺杂氮化硼成功地引入到石墨化炭/硫正极体系中，建立了对石墨化炭导电性、杂原子掺杂氮化硼孔道结构及表面性质调控的策略及测试手段，可控制备高孔隙、高导电、强极性硫载体，借助物理吸附、化学吸附、催化转化三重作用，协同增效，实现硫物种的高效固载和利用，解决了单质硫作为电极材料稳定性差、硫利用率低等问题，大幅提升了锂硫电池硫正极的性能；研究了石墨化炭/杂原子掺杂氮化硼复合材料作为新型硫载体对多硫化锂的物理吸附、化学吸附、催化转化作用；发展了原位表征技术（原位XRD、原位拉曼光谱等），对锂硫电池充放电过程中硫物种的相变进行了原位跟踪，揭示了石墨化炭/杂原子掺杂氮化硼载体材料的导电性、孔隙率、极性等与硫正极电化学性能之间的关联规律，为构建新型高性能锂硫电池提供指导。本项目围绕这一方向在ACS Cent. Sci., Adv. Mater., J. Mater. Chem. A, Chem. Eng. J., Nano Res.等期刊共发表SCI收录的研究性论文23篇；申请国内专利11项，获得授权7项。在国际/国内会议中口头报告18次，培养博士研究生4名，硕士研究生4名。