石墨烯/多孔硅/石墨烯夹层结构设计及其充放电过程研究

Silicon has been considered as a promising candidate for lithium ion batteries due to the highest theoretical capacity of 4200 mAh/g, which is ten time than that commercial graphite carbon anode. The practical application of Si-based anodes, however, is still hindered by two critical problems: the relative low electric conductivity and huge volume expansion (~ 400%) during lithium insertion and extraction, leading to the structural degradation and unstable solid electrolyte interphase (SEI) formation. This project will systematically investigate and solve the key fundamental issues through the introduction of graphene with high electronic conductivity and mechanical stability as the encapsulation layers, producing the porous silica sealed between graphene nanosheets (not the simply mixture) sandwiched nanostructures through sol-gel, chemical vapor deposition and magnesiothermic reduction approaches. The topics include two main parts: such as sol-gel-derived formation of graphene/porous silicon/graphene sandwiched nanostructures, and fabrication of graphene/porous silicon/graphene mesoporous architectures through spatially confined chemical vapor deposition. It is supposed to investigate the electrochemical reaction mechanism and relationship between structural design of composites, surface properties and performance during charge and discharge process. They are useful to supply experimental evidence for optimization and promotion of silicon-based anodes with large Coulombic efficiency, high capacity, long cycling life and excellent rata capability.

硅基材料具有最高的理论比容量（十倍于目前商业化锂离子电池石墨类碳材料），是最具潜力的下一代高能锂离子电池负极材料。然而，低的电导率和充放电过程中巨大的体积膨胀以及结构的粉化、电极材料与集流体的脱离和不稳定的固体电解液界面等限制了其实际应用。本项目拟利用具有高导电性和机械稳定性石墨烯网络为包覆层，利用溶胶-凝胶法、化学气相沉积和镁热还原技术将多孔硅材料封装于二维石墨烯网络夹层中（非传统的简单混合堆积）。项目主要研究内容包括：1）溶胶-凝胶法制备二维石墨烯/多孔硅/石墨烯三明治结构；2）介孔限域空间内化学气相沉积构建石墨烯/多孔硅/石墨烯夹层结构。详细考察这些夹层复合材料的结构设计、表面性质和电化学性能，得到具有高库伦效率、高容量、长循环、大倍率性能与结构、组分的关系。

本项目的总体目标是以高导电性和机械稳定性的碳网络为包覆层，将多孔硅材料封装于碳网络中，研究硅碳复合材料的结构特征、表面性质和电化学性能。通过本项目的实施，系统深入研究了多孔硅与导电碳的构效关系与电化学反应机制。通过材料设计和合成方法的创新，实现了多孔硅与导电碳的设计和调控，如以苯基侨联的有机硅为前驱体，通过前驱体中碳源与Si-O-Si骨架在分子尺度下的复合，获得了高性能的多孔硅基复合材料。探究了硅碳复合材料结构与性能之间的关系，如将硅分别与石墨烯（GO），MXene和碳纳米管（CNTs）整合在碳纳米纤维（CNFs）内部，由于三种导电材料性质的不同，发现Si/CNTs@CNFs具有较为优异的倍率性能，而Si/GO@CNFs表现出高的可逆容量。考察了表面修饰对材料性能的影响，如以硼掺杂诱导互连组装制备的B-SiOC组装体在2 A g-1的情况下，可以稳定循环2000圈。这些结果不仅有利于对硅负极的理解和认识，也为发展优化高比能二次电池负极材料的研究提供了重要的实验依据和的理论指导。