基于Ti4O7/rGO双导电网络气凝胶的柔性自支撑锂硫电池正极材料研究

Aerogels, highly porous three-dimensional nanomaterials with ultrahigh specific surface area, are generally prepared by drying wet gel precursors. Graphene is a two-dimensional carbon nanomaterial with superior conductivity, strength and flexiblity. Graphene oxide (GO) is often used as precursor for graphene aerogel preparations due to its abundant active oxide functional groups and perfect dispersion in solvents. GO is feasible to be reduced into conductive reduced graphene oxide (rGO) by simply methods. Ti4O7, a Magnéli pahse oxide, is testified that it can adsorb polysulfide and Li2S and promote their redox reaction during the charge-discharge cycling of lithium-sulfur battery. In our present proposal, starting from design of the Ti4O7/rGO aerogel with bicontinuous conductive network, we are aiming at providing a flexible freestanding Ti4O7/rGO-S cathode which is free of additional adhesive and current collector but possesses improved capability, cycling stability and Coulombic efficiency. During running this proposal, the optimal parameters and conditions for synthesizing the Ti4O7/rGO aerogels with bicontinous conductive network will be set up, the network structure and physicochemical properties of the Ti4O7/rGO aerogels will be investigated, the relationship among synthetic conditions-network structure-physicochemcial properties of Ti4O7/rGO aerogels will be determined. At the same time, electrochemical behavior of the Ti4O7/rGO-S cathode will be investigated and the effect of the synthetic parameters and composition ratios on the electrochemical properties will be clarified.

气凝胶是具有高比表面积和高度多孔的三维纳米材料，一般通过干燥湿凝胶前体制备。石墨烯是具有优良导电性和柔韧性的二维纳米碳材料。石墨烯的氧化物GO由于富有反应性的含氧官能团且能够良好地分散在溶剂中而常被用作合成石墨烯气凝胶的前体。GO可通过简单的方法还原成为导电的rGO。Ti4O7是一种具有导电性的Magnéli相氧化物，能牢固吸附多硫化物及Li2S并促进其在锂硫电池充放电中氧化还原反应的进行。本项目从Ti4O7/rGO双导电网络气凝胶的设计出发，以获得无需额外粘合剂和集流体且具有更好的循环稳定性、更高容量和库伦效率的柔性自支撑Ti4O7/rGO-S正极为目的，探索制备双导电网络气凝胶的工艺路线和合成条件，考察其结构与物理化学性能，尝试建立合成参数-结构-物理化学性能之间的关系；同时研究Ti4O7/rGO-S正极的电化学过程，阐述合成工艺参数和组成比例等因素对其电化学性能的影响。

锂硫电池由于具有高的理论比容而被认为是最具潜力的新一代二次电池之一，但其实际应用受到多硫化物溶解穿梭和反应动力学迟缓等问题的限制。为了改善这些问题并应对柔性电子器件发展的迫切需求，本项目首先通过水热法制备了有机钛/还原氧化石墨烯复合水凝胶，进而通过冷冻干燥和高温热处理制备了含有Ti4O7的TixOy/ rGO弹性双导电复合气凝胶作为高性能柔性自支撑硫正极载体材料。系统研究了反应物浓度和反应温度对气凝胶的组成、结构和机械性能的影响，提出了优化的TixOy/rGO复合气凝胶的制备工艺。研究结果表明，TixOy尤其是具有电子导电性并对多硫化物的电化学氧化还原具有催化作用的Ti4O7与形成三维多孔框架的rGO协同作用，使锂硫电池的电化学性能得到显著提升。此外，还制备了一系列无机或有机功能组分修饰的功能碳材料用作锂硫电池正极载体或功能插层，对于锂硫电池性能的改善也呈现明显的效果。