具有协同效应的二苯基四硫化物锂﹣硫正极材料的设计与构筑

Lithium-sulfur (Li-S) batteries become one of the most promising high-energy lithium battery systems due to their high specific energy. However, their cycling stability and high specific energy cannot be achieved simultaneously because of the intrinsic issues of sulfur cathode such as insulation of sulfur and dissolution of polysulfides. Therefore, the construction of novel sulfur cathodes is the main route to solve the scientific problems of Li-S batteries. This project aims to design and construct a novel cathode consisting of the active material of diphenyl tetrasulfide with high capacity to increase energy densities of Li-S batteries and self-weaved metal compound nanofibers/carbon nanotubes as current collectors and supports, which have the synergistic effect of “physical confinement” and "chemical adsorption”. The focus of this project lies on the preparation of metal compound nanofibers by an electrospinning technique, which are “self-weaved” with carbon nanotubes to form a binder-free current collector, realizing the integrity of supports and current collectors. The synergistic effect of the “chemical adsorption” between metal sites and lithium phenolate/lithium polysulfides and “physical confinement” of the nanospace in the self-weaved current collector and the electrocatalytic conversion effect of metal compounds are utilized to improve battery cycling performance. At the same time, this project also combines the experimental and characterization data with the theoretical calculation to deduct the basic properties, structural changes, and adsorption behavior of symmetric linear diphenyl tetrasulfide to optimize its electrochemical behavior.

锂-硫电池由于其高比能量而成为下一代高能锂电池的候选者之一。但以单质硫作为正极，其绝缘特性和多硫化物的溶解导致锂-硫电池循环稳定性和高比能量难以兼容。因此，构建新型硫基正极是解决锂-硫电池基本科学问题的主要途径。本项目基于“物理限域”和“化学吸附”协同作用的设计思路，制备自支撑的碳基金属化合物纳米纤维/碳纳米管作为集流体和载体，并创新性地采用具有高理论容量的二苯基四硫化物作为活性材料，构筑高比能锂-硫电池。项目的重点在于制备系列金属化合物纳米纤维，与碳纳米管“自编织”制备成无粘结剂的集流体，实现支撑体和集流体一体化，利用金属位点对苯基硫锂/多硫化锂的“化学吸附”和自编织的孔隙产生的“物理限域”协同提高循环性能，以及金属化合物带来的电催化转化效果。同时，该项目结合实验和表征数据，辅助理论计算，推演基本属性、结构变化和吸附行为，对具有对称线型多硫特性的二苯基四硫化物的电化学行为进行优化研究。

锂硫电池因其具有高的理论比容量（1672 mAh g-1）和理论比能量（2600 Wh kg-1）被认为是最有前景的下一代电池体系，然而硫正极依然面临着剧烈的体积变化和严重的多硫化锂的溶解穿梭问题。含硫-硫键的有机硫材料作为锂硫电池硫衍生物的重要分支，近年来受到了广泛关注。但有机硫化物也存在容量衰减问题，有必要探究其衰减机理以提高其循环稳定性。本项目按计划开展相关研究工作，较好地完成了所制定的研究目标。我们以苯基四硫化物作为正极主体材料，揭示了其衰减机理，并提出使用碳基过渡金属硫化物集流体来吸附放电产物，建立了正极主体和客体材料“材料-属性-性能”之间的关系。同时我们提出了有机无机复合正极并探究了其电化学性能；使用小分子有机硫醇在锂硫电池中构筑稳定的界面，为制备高性能锂硫电池提供新思路。项目完成人在该项目资助下，在Journal of the American Chemical Society，Angewandte Chemie International Edition，Nature Communications，Advanced Science，Advanced Functional Materials等期刊上已发表SCI收录论文39篇，作为第一或通讯作者发表SCI论文20余篇。申请国家发明专利1件，培养已毕业硕士研究生8名，在读博士生1名，均已完成预期目标。