新型多孔碳基材料的复合设计与载硫机制研究

Lithium-Sulfur batteries, composed of the sulfur cathode and lithium metal anode, have the advantages of high energy density, low cost and environmentally friendly characters. They are promising to be the the new generation power supply. However, this system suffers from some critical problems, such as the low electrical conductivity of sulfur and lithium polysulphide dissolution, resulting in the low utilization of active mass and poor cycling performance of the cell.Recent researches have shown that modification of the cathode can remarkably improve the batteries' performance. But, most of these works were focused on the synthetic method and the properites test, and lack the systematic study on the relation between the microstructure of the carrier in cathode and the cell performance. Our work here is based on the design and synthesis of novel nanoporous carbon materials with superhigh surface areas and large pore volumes. And then, apply them as sulfur carriers to prepare the cathode composites. In-situ synchrotron radiation and neutron diffraction will be applied to reveal the relationship between the composites structure and the electrochemistry performance. This work will provide both theroetical instruction and experimenta data for the research of high energy density power supply, and accelerate the development of electric vehicle industry in China.

以单质硫为正极、金属锂为负极的锂硫电池以其高的理论比能量，原料硫廉价、环境友好的特性有望新一代动力电池。但是，由于硫单质导电性差，放电产物多硫化物易溶解耗散，从而导致电池活性物质利用率低，循环性能差，容量逐步衰减。目前的研究发现，通过硫正极的改性可以显著地提高硫正极的导电率并抑制多硫化物的溶解流失，但是这些研究主要集中于材料制备方法和性能分析，对于载体材料的微观结构和化学特性对整体性能的影响尚缺乏系统的研究。本项目拟设计、合成多种具有超高比表面积和大孔容的新型纳米多孔碳材料，并以之为载体，制备碳-硫复合正极材料。利用实时原位同步辐射和先进的中子衍射技术研究并揭示材料的结构与电化学性能之间的关系，为研发高比容量锂硫电池提供重要理论指导和实验依据。该项研究将促进动力锂离子电池在汽车领域的技术发展，对加快实现我国电动汽车的产业化发展和规模化应用将起到推动作用，具有积极和重要的现实意义。

本项目以金属有机骨架（MOFs）材料为前驱体，设计合成了多种新型多孔碳材料，具有丰富的孔道结构与电化学活性位点。通过调控MOF前驱体的拓扑结构、颗粒尺寸，得到金属纳米颗粒负载的多孔碳纳米复合材料，在燃料电池催化、锂离子电池、锂硫电池等相关应用表现出优异的活性，进而与其他多孔碳基底如规则介孔碳、石墨烯等复合，大幅提升了导电性与电化学活性；提出了溶剂辅助配体交换，两相封装-客体导向等新型合成策略，进一步拓展了所得多孔碳材料的孔道结构，促进电化学过程中的质量传输。除MOF衍生碳外，我们还研究了多种其他可作为硫载体的多孔材料，包括硼氮共掺杂碳纳米管/片，共价有机骨架，纯MOF材料等。在此基础上，我们探究了多种载硫机制，提出三种提高锂硫电池性能的策略：1. 构造介孔-微孔分级孔道结构；2. 多孔碳基底中负载活性金属氧化物、硫化物，增强对多硫化物和单质硫的吸附作用；3. 杂原子如N，B，S掺杂多孔碳，改变碳表面电子云分布，增加电化学活性中心。基于这三种策略，我们以所得的一系列多孔碳材料负载单质硫并组装电池，表现出了优异的容量与循环性能。