Begić Srđan, Jónsson Erlendur, Chen Fangfang, Forsyth Maria
ARC Centre of Excellence for Electromaterials Science and Institute for Frontier Materials (IFM), Deakin University Burwood Campus, 221 Burwood Hwy, Burwood, VIC 3125, Australia.
Phys Chem Chem Phys. 2017 Nov 15;19(44):30010-30020. doi: 10.1039/c7cp03389c.
Understanding the electrode-electrolyte interface is essential in the battery research as the ion transport and ion structures at the interface most likely affect the performance of a battery. Here we investigate interfacial structures of three ionic liquids: 1-ethyl-3-methylimidazolium dicyanamide ([Cmim][dca]), 1-butyl-3-methylimidazolium dicyanamide ([Cmim][dca]) and N-butyl-N-methylpyrrolidinium dicyanamide ([Cmyr][dca]) at a charged and uncharged graphene interface using molecular dynamics simulations. We find that these ionic liquids (ILs) behave differently both in the bulk phase and near a graphene interface and we find that this difference is apparent in all types of analyses performed here. First, a partial density analysis in the direction perpendicular to the surface of the electrodes, which, in the cases near a negatively charged graphene, reveals that the pyrrolidinium system is generally more layered than the imidazolium systems. Second, a 2D topographic structure analysis of the IL species in the inner layer near a negatively charged graphene surface, which reveals that the pyrrolidinium system exhibits a quasi-hexagonal surface configuration of the cations, while the imidazolium systems show linearly arranged groups of cations. Third, a 3D orientation-preference analysis of cation rings near the negative graphene electrode, which shows that the pyrrolidinium rings prefer to lie parallel to the electrode surface while the imidazolium rings prefer to stand on the electrode surface at high tilt angles. Extending the imidazolium alkyl chain was found to reduce the number of imidazoliums that can link up into linearly arranged groups in the inner layer 2D structures. Our results support earlier experimental findings and indicate that the interfacial nanostructures may have a significant influence on the electrochemical performance of IL-based batteries.
了解电极 - 电解质界面在电池研究中至关重要，因为界面处的离子传输和离子结构很可能会影响电池的性能。在此，我们使用分子动力学模拟研究了三种离子液体：1 - 乙基 - 3 - 甲基咪唑二氰胺盐（[Cmim][dca]）、1 - 丁基 - 3 - 甲基咪唑二氰胺盐（[C4mim][dca]）和N - 丁基 - N - 甲基吡咯烷二氰胺盐（[C4mpyr][dca]）在带电和不带电的石墨烯界面处的界面结构。我们发现，这些离子液体在本体相和靠近石墨烯界面处的行为有所不同，并且我们发现在此处进行的所有类型分析中这种差异都很明显。首先，在垂直于电极表面的方向上进行的部分密度分析表明，在靠近带负电的石墨烯的情况下，吡咯烷鎓体系通常比咪唑鎓体系更具分层性。其次，对带负电的石墨烯表面附近内层中的离子液体物种进行的二维地形结构分析表明，吡咯烷鎓体系呈现出阳离子的准六边形表面构型，而咪唑鎓体系则显示出阳离子的线性排列基团。第三，对负石墨烯电极附近阳离子环的三维取向偏好分析表明，吡咯烷鎓环倾向于与电极表面平行排列，而咪唑鎓环则倾向于以高倾斜角立在电极表面上。研究发现，延长咪唑鎓烷基链会减少在内层二维结构中能够连接成线性排列基团的咪唑鎓数量。我们的结果支持了早期的实验发现，并表明界面纳米结构可能对基于离子液体的电池的电化学性能有重大影响。
