Lee Hyejin, Hwang Sunwook, Kim Minju, Kwak Kyungwon, Lee Jaeho, Han Young-Kyu, Lee Hochun
Department of Energy Science and Engineering, DGIST, Daegu 42988, Republic of Korea.
Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), and Department of Chemistry, Korea University, Seoul 02841, Republic of Korea.
J Phys Chem Lett. 2020 Dec 17;11(24):10382-10387. doi: 10.1021/acs.jpclett.0c03235. Epub 2020 Nov 25.
The marked difference in the ionic conductivities of linear carbonate (LC) electrolyte solutions despite their similar viscosities and permittivities is a long-standing puzzle. This study unraveled the critical impact of solvent conformational isomerism on salt dissociation in 0.1-3.0 M LiPF dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) solutions using Raman and dielectric relaxation spectroscopies. The extent of salt dissociation in the LC solutions, which decreased in the order DMC > EMC > DEC, is closely related to the fraction of polar LC conformers, as this conformer participates in Li ion solvation more readily than the nonpolar counterpart. Our first-principles calculations corroborated that the conformer facilitates free ion formation more than the conformer, and the extent of this effect decreased in the order DMC > EMC > DEC. This study provides an avenue for the design of highly conductive electrolytes by exploiting the conformational isomerism of solvent molecules.
尽管线性碳酸酯（LC）电解质溶液的粘度和介电常数相似，但其离子电导率却存在显著差异，这是一个长期存在的难题。本研究利用拉曼光谱和介电弛豫光谱，揭示了溶剂构象异构对0.1 - 3.0 M 六氟磷酸锂（LiPF）在碳酸二甲酯（DMC）、碳酸甲乙酯（EMC）和碳酸二乙酯（DEC）溶液中盐解离的关键影响。LC溶液中盐的解离程度按DMC > EMC > DEC的顺序降低，这与极性LC构象体的比例密切相关，因为这种构象体比非极性构象体更容易参与锂离子溶剂化。我们的第一性原理计算证实，该构象体比构象体更有利于自由离子的形成，且这种效应的程度按DMC > EMC > DEC的顺序降低。本研究为通过利用溶剂分子的构象异构来设计高导电性电解质提供了一条途径。
