Koo Bonhyeop, Hwang Sunwook, Ahn Kyoung Ho, Lee Chulhaeng, Lee Hochun
Department of Energy Science and Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu 42988, Republic of Korea.
Electrolyte Material Team, Advanced Cell Research Center, LG Energy Solution, Daejeon 34122, Republic of Korea.
J Phys Chem Lett. 2024 Mar 28;15(12):3317-3322. doi: 10.1021/acs.jpclett.4c00545. Epub 2024 Mar 18.
Acetonitrile (AN) electrolyte solutions display uniquely high ionic conductivities, of which the rationale remains a long-standing puzzle. This research delves into the solution species and ion conduction behavior of 0.1 and 3.0 M LiTFSI AN and propylene carbonate (PC) solutions via Raman and dielectric relaxation spectroscopies. Notably, LiTFSI-AN contains a higher fraction of free solvent uncoordinated to Li ions than LiTFSI-PC, resulting in a lower viscosity of LiTFSI-AN and facilitating a higher level of ion conduction. The abundant free solvent in LiTFSI-AN is attributed to the lower Li-solvation power of AN, but despite this lower Li-solvation power, LiTFSI-AN exhibits a level of salt dissociation comparable to that of LiTFSI-PC, which is found to be enabled by TFSI anions loosely bound to Li ions. This work challenges the conventional notion that high solvating power is a prerequisite for high-conductivity solvents, suggesting an avenue to explore optimal solvents for high-power energy storage devices.
乙腈（AN）电解质溶液具有独特的高离子电导率，其原理长期以来一直是个谜。本研究通过拉曼光谱和介电弛豫光谱深入研究了0.1 M和3.0 M双三氟甲烷磺酰亚胺锂（LiTFSI）的乙腈和碳酸丙烯酯（PC）溶液的溶液物种和离子传导行为。值得注意的是，与LiTFSI-PC相比，LiTFSI-AN中未与锂离子配位的游离溶剂比例更高，导致LiTFSI-AN的粘度更低，并促进了更高水平的离子传导。LiTFSI-AN中丰富游离溶剂归因于乙腈较低的锂溶剂化能力，尽管锂溶剂化能力较低，但LiTFSI-AN表现出与LiTFSI-PC相当的盐解离水平，发现这是由与锂离子松散结合的双三氟甲烷磺酰亚胺（TFSI）阴离子实现的。这项工作挑战了高溶剂化能力是高电导率溶剂的先决条件这一传统观念，为探索高功率储能装置的最佳溶剂提供了一条途径。
