基于Nb2O5协同构建离子/电子混合导体型宿主材料及其对多硫化物的吸附-催化研究

Among the next-generation energy storage systems, lithium–sulfur batteries (LSB) have attracted substantial attention because of their high theoretical energy density. Despite considerable merits, LSB are found to be plagued with rapid capacity fading and fast self-discharge during cycling. These unpleasant problems mainly result from the poor electronic/ionic conductivity of sulfur, the shuttle effect of lithium polysulfides (LiPSs), and the volumetric variation of sulfur upon lithiation/delithiation processes. In this project, host materials that containing mixed Li+/e- motion property, free space and robust interface structure in one single system are designed and collaboratively constructed baseed on the use of Nb2O5 and highly conductive networks such as graphene and hollow carbon nanofiber. Of particular note is that the selected hollow Nb2O5 microspheres (HNB) not only exhibits ultrafast Li+ motion property due to its unique room-and-pillar NbO6/NbO7 framework structure, but also demonstrates moderate polar affnities to the LiPSs. And the highly conductive networks can accelerate the electron transport and benefit the electrochemical reaction kinetics of the whole electrode. In addition, the large void space in HNB not only allows a high loading of sulfur but also significantly accommodates the volume expansion of active materials during lithiation process. The influence mechanism of the mixed electronic-ionic conducting system on the electrode kinetics will be investigated by employing various in(ex)-situ technologies. Finally, combining with theory simulation, the chemical adsorption and electrocatalysis of Nb2O5 for LiPSs will be systematically analyzed. This project will theoretically support the design and preparation of mixed electronic-ionic conducting host materials for LSB. And it has important theoretical significance and extensive application prospects in LSB with decent electrochemical performance and high sulfur loading.

锂硫电池（LSB）具有极高的理论能量密度，在新一代储能电池中发展潜力巨大。硫正极导电性差，锂化过程体积膨胀严重和多硫化物（LiPSs）的穿梭效应是当下LSB所面临的核心问题。本项目拟基于具有良好本征离子扩散能力的Nb2O5，集石墨烯（G）/中空碳纤维（HCNF）等导电网络、微米级空腔和稳定电极界面结构于一体，协同构建Nb2O5微米空心球（HNB）与G、HCNF间离子/电子混合导体硫正极宿主材料。目标结构兼具高效的离子/电子传输，又能有效锚定LiPSs阴离子；同时HNB中的预留微米级空腔既可保证高硫负载量亦能显著缓解体积效应带来的导电网络失效和电极龟裂等问题。进一步借助各类（非）原位表征技术并结合理论计算建立构效关系，揭示Nb2O5对LiPSs的吸附、催化机理，探明离子/电子混合导体结构对LSB性能的影响规律，为高硫负载量以及优异LSB体系的构筑提供可靠的实验基础和科学依据。

锂硫电池（LSB）具有极高的理论能量密度，在新一代储能电池中发展潜力巨大。硫正极导电性差，锂化过程体积膨胀严重和多硫化物（LiPSs）的穿梭效应是当下LSB所面临的核心问题。我们集碳纤维集流体、氮掺杂碳等导电网络和稳定电极界面结构于一体，协同构建了系列高性能硫正极载体及隔膜修饰材料。例如：（1）基于Nb2O5独特“室柱式”结构所具有的高效离子扩散能力，制备了Nb2O5自分支纳米阵列，该结构在保持柔性电极界面稳定性的同时可以暴露出更为丰富的吸附-催化位点；（2）创新性地将轻质g-C3N4薄膜和由聚（3,4-亚乙基二氧噻吩）组成的导电聚合物（CP）有机的集成在柔性碳布（CC）骨架上，将催化剂与LiPSs的作用方式由传统的“点对面”模式调控为更为高效的“面对面”模式；（3）通过酵解及预构筑技术，分别制备了含N, O共掺杂的三维多孔碳基材料、Co@CoO@N-C/rGO气凝胶以及耦合有莫特-肖特基丰富异质界面的N掺杂碳纳米带，探究了它们对LiPSs的独特吸附-催化转化机理。基于上述研究内容，我们在包括Advanced Energy Materials, Journal of Materials Chemistry A, Chemical Engineering Journal 等国际知名期刊上发表学术论文8篇。以上研究成果为实现锂硫电池用高效电催化剂的精准制备提供了理论参考，同时，也为高硫负载量以及优异LSB体系的构筑提供了可靠的实验基础和科学依据。