Shimizu Masahiro, Usui Hiroyuki, Sakaguchi Hiroki
Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, 4-101 Minami, Koyama-cho, Tottori 680-8552, Japan and Center for Research on Green Sustainable Chemistry, Tottori University, 4-101 Minami, Koyama-cho, Tottori 680-8552, Japan.
Phys Chem Chem Phys. 2016 Feb 21;18(7):5139-47. doi: 10.1039/c5cp05008a.
As the development of high energy-density Li-ion batteries moves ahead, ensuring safety of the batteries has become increasingly important. Among the unique physicochemical properties of ionic liquids, thermal stability can be one of the answers to the challenge. The use of ionic liquids, however, causes critical issues concerning the kinetics of Li-ion transfer at the electrode-electrolyte interface. In the present study, ionic liquids consisting of 1-((2-methoxyethoxy)methyl)-1-methylpiperidinium (PP1MEM) or 1-hexyl-1-methylpiperidinium (PP16) and bis(trifluoromethanesulfonyl)amide (TFSA) were applied to an electrolyte for Li-ion batteries, and we investigated the effect of cation structure on interfacial Li-ion transfer using Li4Ti5O12 as a model electrode by means of Raman spectroscopy and electrochemical impedance spectroscopy. It was found that the ether functional group in the PP1MEM cation has the meaningful function; the cation structure reduces the electrostatic interaction between the Li ion and TFSA anions in an ionic liquid electrolyte. The solvation number of the TFSA anion per Li ion consequently became smaller than that in PP16-TFSA, and the lower solvation number in PP1MEM-TFSA allowed the facile Li-ion diffusion in the electrolyte bulk rather than the interfacial Li-ion transfer and significantly improved the rate performance. The results offer the prospect of utilization of PP1MEM-TFSA as an electrolyte solvent. The knowledge obtained from this study contributes to the development of next-generation Li-ion batteries having both high energy density and high safety.
随着高能量密度锂离子电池的发展，确保电池安全变得越来越重要。在离子液体独特的物理化学性质中，热稳定性可能是应对这一挑战的答案之一。然而，离子液体的使用引发了有关电极-电解质界面处锂离子转移动力学的关键问题。在本研究中，由1-((2-甲氧基乙氧基)甲基)-1-甲基哌啶鎓（PP1MEM）或1-己基-1-甲基哌啶鎓（PP16）与双(三氟甲磺酰)亚胺（TFSA）组成的离子液体被应用于锂离子电池的电解质中，并且我们通过拉曼光谱和电化学阻抗谱，以Li4Ti5O12作为模型电极，研究了阳离子结构对界面锂离子转移的影响。结果发现，PP1MEM阳离子中的醚官能团具有重要作用；阳离子结构降低了离子液体电解质中锂离子与TFSA阴离子之间的静电相互作用。因此，每个锂离子的TFSA阴离子溶剂化数变得比PP16-TFSA中的小，并且PP1MEM-TFSA中较低的溶剂化数使得锂离子在电解质本体中易于扩散，而不是在界面处进行锂离子转移，从而显著提高了倍率性能。这些结果为将PP1MEM-TFSA用作电解质溶剂提供了前景。从本研究中获得的知识有助于开发兼具高能量密度和高安全性的下一代锂离子电池。
