Liyana-Arachchi Thilanga P, Haskins Justin B, Burke Colin M, Diederichsen Kyle M, McCloskey Bryan D, Lawson John W
Department of Chemical and Bimolecular Engineering , University of California , Berkeley , California 94720 , United States.
J Phys Chem B. 2018 Sep 13;122(36):8548-8559. doi: 10.1021/acs.jpcb.8b03445. Epub 2018 Sep 4.
The structure and transport properties of electrolyte solutions of 1,2-dimethoxyethane (DME) having salts of Li with bis(trifluoromethanesulfonyl)imide ([TFSI]) or Na with [TFSI] are investigated with polarizable molecular dynamics and experiments. Polarizable force fields for Li and Na with DME and [TFSI] were developed based on quantum chemistry calculations, ab initio molecular dynamics simulations, and thermodynamic liquid-state properties. Simulation results for density, viscosity, self-diffusion coefficient, and conductivity of the electrolytes all agree well with the trends and magnitudes of available experimental data for a wide range of salt concentrations. As the concentration of salt increases, the electrolytes become more viscous and molecular species become less mobile. Ionic conductivity does not change monotonically with salt concentration and exhibits a maximum between 0.5 and 1.0 M for both Li[TFSI] and Na[TFSI] electrolytes. Comparatively, both cations are solvated by 5-6 DME or [TFSI] oxygen atoms and exhibit similar diffusivities and conductivities. The solvation shell of Na is found to be more weakly bound and to have a lower binding residence time than that of Li. The transport of Li therefore is more vehicular, through the motion of the solvation shell, while the transport of Na is based more on exchange, through the replacement of solvating species. The atomistic insight provided by this work can be used as the basis for future rational design of improved electrolyte solvents for lithium-oxygen, sodium-oxygen, and lithium-sulfur batteries.
采用可极化分子动力学和实验方法，研究了含有锂双（三氟甲磺酰）亚胺盐（[TFSI]）或钠双（三氟甲磺酰）亚胺盐（[TFSI]）的1,2 - 二甲氧基乙烷（DME）电解质溶液的结构和传输性质。基于量子化学计算、从头算分子动力学模拟和热力学液态性质，开发了锂、钠与DME和[TFSI]的可极化力场。对于各种盐浓度下电解质的密度、粘度、自扩散系数和电导率的模拟结果，与现有实验数据的趋势和量级均吻合良好。随着盐浓度的增加，电解质变得更加粘稠，分子种类的流动性降低。离子电导率并不随盐浓度单调变化，对于Li[TFSI]和Na[TFSI]电解质，在0.5至1.0 M之间均出现最大值。相比之下，两种阳离子均被5 - 6个DME或[TFSI]氧原子溶剂化，表现出相似的扩散率和电导率。发现钠的溶剂化壳层结合较弱，结合停留时间比锂的更低。因此，锂的传输更多是通过溶剂化壳层的移动，而钠的传输更多基于交换，即通过溶剂化物种的替换。这项工作提供的原子层面的见解可作为未来合理设计用于锂氧、钠氧和锂硫电池的改进电解质溶剂的基础。
