It has recently been demonstrated that aqueous lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium chloride (LiCl) solutions can form stable liquid-liquid biphasic systems when both elec- trolyte phases have sufficiently high concentrations. In this work, we combine molecular dynamics simulations and experimental analysis to investigate what drives the formation of the interface and how the interfacial molecular structure correlates with its thermodynamic stability. We observe that at the liquid-vapour interface, TFSI− anions exhibit surfactant-like properties, leading to a reduction in surface tension and an increase in interfacial thickness. On the contrary, the interfacial stability of the LiTFSI-LiCl biphasic systems increases with the concentration of both salts, as evidenced by the increasing surface tension and decreasing interfacial thickness. The opposing effects that the ionic concentration has on the thermodynamic stability of the different interfaces are linked to the anions’ interfacial adsorption/desorption, which in turn affects the number and strength of water-water hy- drogen bonds, the interfacial molecular structure and the diffusion of cations across the interface. Finally, calculations and experiments indicate that the liquid-liquid separation is driven primarily by the concentration of LiCl, and is the result of a ’salting out’ effect.

中文翻译：

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水性 LiTFSI-LiCl 界面的稳定性和结构

最近的研究表明，当两种电解质相都具有足够高的浓度时，双（三氟甲磺酰）亚胺锂（LiTFSI）和氯化锂（LiCl）水溶液可以形成稳定的液-液双相体系。在这项工作中，我们结合分子动力学模拟和实验分析来研究驱动界面形成的因素以及界面分子结构与其热力学稳定性的关系。我们观察到，在液-气界面，TFSI−阴离子表现出类似表面活性剂的特性，导致表面张力降低和界面厚度增加。相反，LiTFSI-LiCl双相体系的界面稳定性随着两种盐浓度的增加而增加，表面张力的增加和界面厚度的减少证明了这一点。离子浓度对不同界面热力学稳定性的相反影响与阴离子界面吸附/解吸有关，进而影响水-水氢键的数量和强度、界面分子结构和阳离子穿过界面的扩散。最后，计算和实验表明液-液分离主要由氯化锂的浓度驱动，并且是“盐析”效应的结果。