Chen Ying, Jaegers Nicholas R, Wang Hui, Han Kee Sung, Hu Jian Zhi, Mueller Karl T, Murugesan Vijayakumar
Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States.
Joint Center for Energy Storage Research (JCESR), Lemont, Illinois 60439, United States.
J Phys Chem Lett. 2020 Aug 6;11(15):6443-6449. doi: 10.1021/acs.jpclett.0c01447. Epub 2020 Jul 28.
One of the main impediments faced for predicting emergent properties of a multivalent electrolyte (such as conductivity and electrochemical stability) is the lack of quantitative analysis of ion-ion and ion-solvent interactions, which manifest in solvation structures and dynamics. In particular, the role of ion-solvent interactions is still unclear in cases where the strong electric field from multivalent cations can influence intramolecular rotations and conformal structural evolution (i.e., solvent rearrangement process) of low permittivity organic solvent molecules on solvation structure. Using quantitative H, F, and O NMR together with F nuclear spin relaxation and diffusion measurments, we find an unusual correlation between ion concentration and solvation structure of Mg(TFSI) salt in dimethoxyethane (DME) solution. The dominant solvation structure evolves from contact ion pairs (i.e., [Mg(TFSI)(DME)]) to fully solvated clusters (i.e., [Mg(DME)]) as salt concentration or as temperature . This transition is coupled to a phase separation, which we study here between 0.06 and 0.36 M. Subsequent analysis is based on an explanation of the solvent rearrangement process and the competition between solvent molecules and TFSI anions for cation coordination.
预测多价电解质的涌现性质（如电导率和电化学稳定性）面临的主要障碍之一是缺乏对离子-离子和离子-溶剂相互作用的定量分析，这些相互作用体现在溶剂化结构和动力学中。特别是，在多价阳离子产生的强电场会影响低介电常数有机溶剂分子在溶剂化结构上的分子内旋转和构象结构演化（即溶剂重排过程）的情况下，离子-溶剂相互作用的作用仍不清楚。通过使用定量的氢、氟和氧核磁共振以及氟核自旋弛豫和扩散测量，我们发现了二甲基乙二醚（DME）溶液中Mg（TFSI）盐的离子浓度与溶剂化结构之间的异常相关性。随着盐浓度或温度的变化，主要的溶剂化结构从接触离子对（即[Mg（TFSI）（DME）]）演变为完全溶剂化的簇（即[Mg（DME）]）。这种转变与相分离相关联，我们在此研究了0.06至0.36 M之间的相分离。后续分析基于对溶剂重排过程以及溶剂分子与TFSI阴离子在阳离子配位方面竞争的解释。
