功能化石墨烯的量子电容的理论研究

As a novel kind of energy storage component，supercapacitor has many advantages of high specific capacitance, high power density, green environmental protection and long cycle life. The working electrode is the key part to effect the performance of supercapacitor, and the preparation of electrode material with high energy density is the important investigation in the development of supercapacitor. Graphene is considered as one of the most promising electrode materials for supercapacitors due to its excellent physic and chemical performance. Despite many advantages of graphene-based electrodes, there remains a major limitation, which is low value of specific capacitance. This limitation is observed in graphene-based electrodes due to their low quantum capacitance. An effective method is the functionalization of graphene aiming to increasing its capacitive properties. Using combined first-principles and classical molecular dynamics calculations, this research plan here will explore the effect of the coexistence of different functional factors on the quantum capacitance of graphene, which contain defect, functional groups and dopants. Furthermore, we will investigate the variations of double layer capacitance of the functionalized graphene aiming to explore the influence of the promotion of quantum capacitance on enhancing the total interfacial capacitance. Therefore, this study will provide the theoretical guidelines and scientific bases for developing graphene-based supercapacitors with high energy density, high specific capacitance and good stability.

超级电容器作为一种新型储能装置，具备高比电容、高功率密度、绿色环保、循环寿命长等优点。其中，工作电极是超级电容器的重点组成部分，制备出兼有高能量密度的电极材料是当前超级电容器的研究重点。石墨烯由于其优良的物理化学特性被认为是最适合用于超级电容器的电极材料之一而在近年来得到广泛研究。然而，石墨烯较低的量子电容限制了其作为电极材料的应用。对石墨烯进行功能化以提高其电容特性是一种有效的解决途径。本项目采用第一性原理和经典分子动力学计算方法，系统的研究不同类型缺陷、功能团修饰和掺杂杂质等功能化条件共存对石墨烯量子电容的协同调控机制。通过建立超级电容器微结构，探究功能化条件对石墨烯双层电容的影响，对比分析量子电容的提升对增大界面电容的贡献。本研究将为发展高电容、高能量密度和稳定循环性能的石墨烯基超级电容器提供理论指导和科学依据。

石墨烯被认为是最适合用于超级电容器的备选电极材料之一，在近年来得到广泛研究。然而，纯石墨烯作为电极材料，它的双电层理论比电容并不大，合成石墨烯的过程中容易造成团聚堆叠现象。本课题基于密度泛函理论，研究了不同功能化条件对石墨烯基底量子电容的提升，分析其提升机理。首先，我们探究了空位缺陷和Stone-Wales（SW）缺陷的出现对石墨烯量子电容的影响，结果发现空位缺陷对量子电容的提升更为显著。空位缺陷的引入，使石墨烯的最大量子电容从原来的21.37 μF/cm2增大到 120.72 μF/cm2，表面电荷储存量从原来的12.58 μC/cm2增大到40.14 μC/cm2。其次，我们探究了缺陷和杂质（B、N、Al、Si、P、S）共存对石墨烯量子电容的影响。结果表明在负电势范围内，Si掺杂的空位缺陷石墨烯表现最为突出，其量子电容和表面电荷储存量高达169.76 μF/cm2和-43.22 μC/cm2，可作为不对称电极超级电容器的负极材料。而在正电势范围内，Al掺杂的空位缺陷石墨烯的量子电容（79.89 μF/cm2）和表面电荷储存量（22.86 μC/cm2）最大，可应用为不对称电极超级电容器的正极材料。掺杂的SW缺陷石墨烯的量子电容及电荷储存能力都不及掺杂的空位缺陷石墨烯。总的来说，杂质和缺陷共存对石墨烯量子电容的提升效果优于缺陷石墨烯。接着，我们探究了缺陷和杂质浓度对石墨烯量子电容的影响。结果表明，量子电容的值并不是随着掺杂浓度的提高单调递增的。最后，我们探究了过渡金属杂质（Ti、V、Cr、Mn、Co、Ni）和邻近C元素的杂质（N、P、S）共掺杂对石墨烯量子电容的影响。结果表明，过渡金属Ti元素的共掺杂效果最好，在正电势范围内表现出了最大的量子电容（239.84 μF/cm2）和最高的电荷储存量（52.60 μC/cm2）。因此，Ti与N/P/S共掺杂的石墨烯作为不对称超级电容器的正极材料具有很大的应用前景。通过计算各种功能化石墨烯的电子结构，我们发现量子电容的变化趋势和体系的电子态密度在费米能级附近的变化趋势是一致的，这说明不同功能化条件改变费米能级附近的电子结构对量子电容的表现起着主导作用。