石墨烯基双电层电容器储能机理的计算机模拟与研究

The supercapacitor is a highly efficient and reliable energy storage device, which features numerous advantages over the traditional Li-ion battery. However, the widespread commercialization of supercapacitors suffers from its low energy density. Nowadays, extensive researches indicate two possible solutions to this problem that are understanding the charge storage mechanism and developing novel electrode materials. Benefiting from the state-of-art R&D achievements, this project is designed to combine computer simulations with experiments to study double layer capacitors, typically consisting of graphene as electrodes and ionic liquids as electrolytes. The detailed research plan is as follows. Firstly, a joint approach of the fist principle calculation and the experiment characterization is to be applied to determine defect structures of graphene. On the basis of specific knowledges of various defects, the fist principle calculation is then employed to develop the classical force field between defective graphene and ionic liquids. Secondly, molecular models of graphene will be built on a large scale, which facilitates the investigation using molecular dynamics methods into the self-folding and aggregation behaviors of graphene layers in ionic liquids. At last, molecular simulations of microporous carbon- and graphene-based capacitor systems can be performed to study and differentiate their distinct charge storage mechanisms. In particular, the excellent capacitance of graphene that is often observed from electrochemical tests is to be explained in view of its unique layered structure. The objective of the entire project is to completely reveal the charge storage mechanism of double layer capacitors, which can be then referred to as an essential criterion in order to predict optimal nanostructures of electrode materials possessing high capacitance. In all, the fundamental understanding gained from this research work is of great value to the development of high performance supercapacitors in the near future.

超级电容器是一种高效可靠的电能存储器件，其诸多性能优势是传统锂离子电池所不具备的。然而，较低的能量密度是限制超级电容器推广应用的一大技术瓶颈。当前大量研究表明，明确双电层电容储能机理和开发新型电极材料是解决这一难题的两个关键点。借鉴国际前沿研究成果，本项目拟采用计算机模拟与实验验证相结合的方法来研究以石墨烯离子液体为代表的双电层电容系统。具体内容包括：结合实验表征与第一性原理计算来确定石墨烯表面多种缺陷结构，并拟合含缺陷石墨烯与典型离子液体之间的经典力场；构建大尺度石墨烯分子模型，利用分子动力学研究石墨烯片层在离子液体中的的自折叠行为和堆积现象；分别模拟石墨烯和微孔炭离子液体电容系统，对比两者储能机理的异同，着重从石墨烯独特的片层结构的角度来诠释其优异的电容性能。本项目旨在深入揭示双电层电容的储能机理，预测大电容量电极材料的最优纳米结构，为高性能超级电容器的研发奠定坚实的理论基础。

该项目经过对石墨烯基超级电容体系的电极过程的典型问题进行了针对性研究，揭示了材料制备和器件组装对电容器性能的影响和机理，对当今电容器产业的技术升级和工艺改进提供了可靠依据。该项目主要研究成果包含利用实验与模拟相结合的方法阐明了石墨烯双电层电容器的充放电机理（Journal of Power Sources 268 (2014) 604-609）。在此基础上，完成了对石墨烯二维电极材料特殊的传质机理（ACS Appl. Mater. Interfaces, 2016, 8 (1), pp 321–332），同时和一维碳纳米管材料的快速传质行为进行了对比（Journal of Membrane Science 493 (2015) 599-604）。与此相关的成果还包括了微孔碳的孔结构对分子吸附扩散的影响（Molecular Simulation 42 (2016) 776-782），以及将相似的并行化分子动力学方法应用到了有机膜的物理化学性质模拟（Applied Surface Science 362 (2016) 441-447）。