原位构筑三维多孔石墨烯化学固定纳米硫化锂复合材料及结构性能调控

Lithium sulfide is considered as an attractive cathode material for Li/S batteries due to the high theoretical specific capacity (1166 mAh/g) and excellent structural stability. It can be paired with different kinds of lithium metal free materials, such as the high capacity tin and silicon anodes. However, the electrochemical performance of the lithium sulfur cathode is hindered by its poor electrical conductivity, shuttle effect of polysulfides and the large voltage barrier on the initial charge. Therefore, the design of conductive matrix turns out to be the key to improve the coulombic efficiency and cycling performance of the lithium-sulfur batteries. Herein, three-dimensional porous grahene/nano-sized lithium sulfide composites are designed and synthesized by in-situ method. In this proposal structure, the lithium sulfide is uniformly distributed in the graphene host with good sequestration. In addition, the dissolution of the sulfide anions is effectively controlled and the electron and ion transfer rates are improved after in-situ activation and polymer coating. This proposal will clarify the associations between the micro-structure and electrochemical properties, and analyze the lithium storage mechanism in the suggested three-dimensional porous grahene/nano-sized lithium sulfide composites.

硫化锂具有较高的理论容量、结构稳定，可与锡、硅等高容量非锂负极配对，被认为是极具潜力的锂硫电池正极材料。针对硫化锂导电性差、聚硫离子穿梭及首次充电存在较高势垒等问题，基于硫正极的导电结构设计及包覆改性是提高锂硫电池库伦效率和循环性能的关键。本项目通过原位合成手段构筑的三维多孔石墨烯化学固定纳米硫化锂复合材料，一方面可以实现硫化锂的共价键固定和均匀分散，另一方面通过原位活化和包覆改性，可抑制中间产物的溶解流失，大幅提高材料的离子和电子传输速率。在此基础上，本项目将研究纳米硫化锂的结构与储锂性能之间的关联，探索该复合正极在锂硫电池中的电化学反应机制。

硫化锂具有较高的理论容量、结构稳定，被认为是极具潜力的锂硫电池正极材料。针对硫化锂导电性差、聚硫离子穿梭及首次充电存在较高势垒等问题，基于硫正极尺寸的纳米化和导电结构设计是提高锂硫电池库伦效率和循环性能的关键。本项目从插层剥离法快速制备薄层石墨烯入手，然后分别设计制备了石墨烯气凝胶负载Li2S@Li3PS4复合材料、原位反应制备石墨烯气凝胶/纳米Li2S、一步溶剂热法制备石墨烯/纳米Li2S三种复合硫正极材料，通过一系列材料物相、微观结构、组分形貌及电性能测试表征，揭示了材料的结构演变过程，总结了纳米硫化锂复合正极的电性能改善机理。此外，利用氧化石墨烯改性传统聚烯烃隔膜用作复合隔膜，显示出对锂硫电池穿梭效应良好的抑制效果，并对其电性能改善机理进行了详细研究。