Molecular Structure, Chemical Exchange, and Conductivity Mechanism of High Concentration LiTFSI Electrolytes
Molecular Structure, Chemical Exchange, and Conductivity Mechanism of High Concentration LiTFSI Electrolytes
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DOI：
10.1021/acs.jpcb.9b10795
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发表时间：
2020-03-12
影响因子：
3.3
通讯作者：
Kuroda, Daniel G.
中科院分区：
文献类型：
--
作者：
Kankanamge, Susith R. Galle;Kuroda, Daniel G.
高浓度锂电解质是制备高能量密度和高压锂电池的理想材料。最近的研究表明，限制电解质中的自由溶剂分子可以防止电池电极的退化。然而，对这种电解质体系的结构和动力学的分子水平知识是有限的，特别是基于典型有机碳酸盐的电解质。本文采用线性、时间分辨振动光谱和计算方法研究了锂二（三氟甲磺酰）亚胺在含羰基溶剂中的相互作用和运动。我们的研究结果表明，三种高浓度电解质的整体结构和形态相似。然而，由于二聚体的形成，循环碳酸盐基电解质呈现出额外的相互作用。时间分辨研究表明，在线性分子组成的电解质中，溶剂分子的结构运动具有相似且快速的动力学，而由环状溶剂分子组成的电解质由于二聚体的形成而表现出较慢的结构变化。此外，还观察到皮秒时间尺度的过程，并将其分配给锂离子溶剂化壳的溶剂分子的配位和配位。这种溶剂交换过程被发现与锂离子和阴离子之间结构的形成和破坏直接相关，从而与传导机制直接相关。总的来说，我们的数据表明溶剂的分子结构对锂离子溶剂化壳的形态和分布没有显著影响。然而，两个相邻锂离子的溶剂分子之间的二聚化似乎产生了一种微观上的有序，这在宏观上表现在电解质的性质上，比如它的粘度。
High concentration lithium electrolytes have been found to be good candidates for high energy density and high voltage lithium batteries. Recent studies have shown that limiting the free solvent molecules in the electrolytes prevents the degradation of the battery electrodes. However, the molecular level knowledge of the structure and dynamics of such an electrolyte system is limited, especially for electrolytes based on typical organic carbonates. In this article, the interactions and motions involved in lithium bis(trifluoromethanesulfonyl)imide in carbonyl-containing solvents are investigated using linear and time-resolved vibrational spectroscopies and computational methods. Our results suggest that the overall structure and the speciation of the three high concentration electrolytes are similar. However, the cyclic carbonate-based electrolyte presents an additional interaction as a result of dimer formation. Time-resolved studies reveal similar and fast dynamics for the structural motions of solvent molecules in electrolytes composed of linear molecules, while the electrolyte made of cyclic solvent molecules shows slower structural changes as a result of the dimer formation. Additionally, a picosecond time scale process is observed and assigned to the coordination and decoordination of solvent molecules from a lithium-ion solvation shell. This process of solvent exchange is found to be directly correlated to the making and breaking of structures between the lithium-ion and the anion and, consequently, to the conduction mechanism. Overall, our data show that the molecular structure of the solvent does not significantly affect the speciation and distribution of the lithium-ion solvation shells. However, the presence of dimerization between solvent molecules of two neighboring lithium-ions appears to produce a microscopic ordering that it is manifested macroscopically in properties of the electrolyte, such as its viscosity.