Quantification of Dynamic Ion Correlations in Highly Concentrated Liquid Electrolytes and of their Implications for Charge and Mass Transport

盐与溶剂的摩尔比高达1：1的高浓度液体电解液在电池和超级电容器的电化学储能领域具有良好的应用前景。由于离子浓度高，阳离子和阴离子的运动具有很强的方向性关联，这对电荷和质量的传输都有影响。输运性质的理论描述可以在Onsager形式和线性响应理论相结合的框架下进行。对于输运参数的实验表征，通常将绝对必要的许多测量变量组合在一起。这可能导致所获得的传输系数的相对较大的不确定区间。本项目超越了这一方法，将电化学测量与基于核磁共振的传输测量相结合，以便在绝对必要时确定另一个测量变量。结合详细的不确定度分析，可以获得选定电解液的Onsager传输系数的非常精确的值，从而获得有关电荷和质量传输特性的准确信息。该方法被应用于三种锂离子导电液体电解质体系：(I)基于有机碳酸盐的高浓度电解液；(Ii)基于环丁砜的高浓度电解液；(Iii)以碳酸盐为盐配位溶剂和氟化醚为非配位溶剂的局域高浓度电解液。通过改变锂盐与不同Li+配位强度的阴离子(FSI-弱，BF4-强)的相互作用，将改变阳离子-阴离子和阳离子-溶剂的相互作用，并考察这些相互作用对电荷和质量传递的影响。在此基础上，将制定指南，说明如何平衡高浓度电解液中的相互作用，从而实现最佳的电荷和质量传输特性。通过这种方式，该项目将有助于更好地从根本上理解高浓度电解液中的相互作用与储能电池中的传输特性之间的关系。

Highly concentrated liquid electrolytes with molar ratios of salt: solvent of up to 1:1 exhibit promising properties for applications in the field of electrochemical energy storage in batteries and supercapacitors. Due to the high ion concentrations, strong directional correlations occur in the movement of cations and anions, which influence both charge and mass transport. A theoretical description of the transport properties can be done in the framework of the Onsager formalism in combination with linear response theory. For the experimental characterization of the transport parameters, typically just as many measured variables are combined as are absolutely necessary. This can lead to relatively large uncertainty intervals for the obtained transport coefficients. The present project goes beyond this approach, as by combining electrochemical measurements with NMR-based transport measurements in order to determine one more measured variable as absolutely necessary. In combination with a detailed uncertainty analysis, very precise values for the Onsager transport coefficients are to be obtained for selected electrolytes, yielding exact information about charge and mass transport properties. This approach is applied to three Li+- conducting liquid electrolyte systems: (i) Highly concentrated electrolytes based on organic carbonates; (ii) Sulfolane-based highly concentrated electrolytes; (iii) Localized high concentration electrolytes with a carbonate as a salt-coordinating solvent and a fluorinated ether as a non-coordinating solvent. Through the variation of lithium salts with anions of different Li+ coordination strength (FSI- weaker, BF4- stronger), cation-anion and cation-solvent interactions will be varied, and the influence of these interactions on charge and mass transport will be examined. Building on this, guidelines are to be drawn up on how the interactions in highly concentrated electrolytes can be balanced in such a way that the best possible charge and mass transport properties are achieved. In this way, the project will contribute to an improved fundamental understanding of the relationships between interactions in highly concentrated electrolytes and transport properties in energy storage cells.