Rustam Sabiha, Intan Nadia N, Pfaendtner Jim
Department of Chemical Engineering, University of Washington, Seattle, Washington 98195, USA.
J Chem Phys. 2021 Oct 7;155(13):134702. doi: 10.1063/5.0066268.
Surface termination on a graphitic surface and the type of electrolytes in lithium-ion batteries (LIBs) play an important part in determining the structure, composition, and thus, the quality of the emergent solid electrolyte interphase. In this paper, we analyze the structure and dynamics of electrolyte molecules in multi-component electrolyte with varying species compositions combinatorially paired with four different graphitic surfaces terminated with hydrogen, hydroxyl, carbonyl, and carboxyl to explore the interplay between surface chemistry and electrolyte dynamics at electrode/electrolyte interfaces. Addition of dimethyl carbonate and fluoroethylene carbonate brought substantial changes in the ethylene carbonate (EC) and LiPF surface population density for hydroxyl and carbonyl surfaces. Strong density oscillation and drastic slowing of the dynamics of the electrolyte molecules at the interface are reported for all the systems. While these observations are universal, carboxyl surfaces have the strongest local and long-range effects. Characterization of the average dipole direction at the interface shows strong orientational preferences of ethylene carbonate molecules. EC molecules are preferred to be oriented either almost parallel or perpendicular to the hydroxyl surface, are tilted between parallel and perpendicular with a higher angle of incidence of the dipole vs surface normal on the carbonyl surface than on the hydroxyl surface, and are oriented perpendicularly against the carboxyl surface. These differences highlight the significant effect of graphite surface termination on the dynamics of the electrolytes and provide insight into the complex interplays between electrolyte species and graphite anode in LIBs.
锂离子电池（LIBs）中石墨表面的表面终止以及电解质的类型在决定新兴固体电解质界面的结构、组成进而质量方面起着重要作用。在本文中，我们分析了多组分电解质中电解质分子的结构和动力学，该电解质具有不同的物种组成，并与四种分别以氢、羟基、羰基和羧基终止的不同石墨表面组合配对，以探索电极/电解质界面处表面化学与电解质动力学之间的相互作用。碳酸二甲酯和氟代碳酸乙烯酯的添加使羟基和羰基表面的碳酸乙烯酯（EC）和LiPF表面种群密度发生了显著变化。据报道，所有系统在界面处电解质分子的动力学都有强烈的密度振荡和急剧减慢。虽然这些观察结果具有普遍性，但羧基表面具有最强的局部和远程效应。界面处平均偶极方向的表征显示碳酸乙烯酯分子有强烈的取向偏好。EC分子倾向于几乎平行或垂直于羟基表面取向，在羰基表面上，其取向在平行和垂直之间倾斜，偶极与表面法线的入射角比在羟基表面上更高，并且垂直于羧基表面取向。这些差异突出了石墨表面终止对电解质动力学的显著影响，并为LIBs中电解质物种与石墨阳极之间复杂的相互作用提供了见解。
