(196f) Structural Reorganization of Ionic Liquid Electrolytes By Charge/Discharge Circle

The behavior of forming layers near the electrode surface is an important topic for the energy storage with ionic liquid (IL) electrolytes ^[1].It is found that surface active ionic liquids (SAILs) and nonamphiphilic ionic liquids (NAILs) form different electric double layer structures near the electrode, which leads to great differences in energy storage between the two kinds of ILs ^[2]. Molecular dynamics (MD) simulation can reproduce the microstructure and process, and can be used to analyze the changes of SAILs or NAILs electric double layers near the electrode. We focus on IL layers near the electrode surface of graphene by MD simulation and get some change rules of charging/discharging circle. The above findings could be used to explain more complex experimental phenomenon and serve as the guide for designing ILs-based electrolytes.

Recent experimental results showed that SAILs show better charge storage performance on charged surface than NAILs ^[2]. Near the positive electrode of [C₄mim][AOT] system, it was found that [AOT]^- would easily enter into the interfacial layer with a V-type conformation during the charging process by MD simulation. Compared with the simulated initial state, there were more V-type anions in the electrolyte after a process of charging and discharging, which is an evidence that the electrolyte was optimized. It provides an alternative way to optimize the IL electrolyte ^[3]. On the other hand, near the negative electrode of [C_nmim][AOT] and [C_nmim][BF₄] systems, the structural transition of imidazolium-based NAILs and SAILs in a two-stage discharge process was discussed ^[4]. The two-stage discharge process of NAILs was more obviously, and it was slightly gentle for SAILs. It was revealed that the quick decrease in electric energy during the first stage of discharging was mainly due to the change of cations shapes near the negative electrode instead of their movement; the slow decrease in electric energy during the second stage of discharging was caused by overscreening and slow movement of cations from the negative electrode. Unlike the conventional view, it is concluded that the large scale movement of ions plays a relatively minor role in releasing electric energy. It will help us to understand the mechanism of energy release and provide a theoretical basis for the rational design of ILs-based electrolytes.

References

[1] Y. Wang, , H. He, , C. Wang, , Y. Lu, , K. Dong, , F. Huo, S. Zhang, Insights into Ionic Liquids: From Z-Bonds to Quasi-Liquids, JACS Au 2 (2022) 543-561.

[2] X. Mao, P. Brown, C. Cervinka, G. Hazell, T. A. Hatton, Self-assembled nanostructures in ionic liquids facilitate charge storage at electrified interfaces, Nature Materials 18 (2019) 1350-1357.

[3] K. Zhang, G. Zhou, T. Fang, K.Jiang, X. Liu, Structural Reorganization of Ionic Liquid Electrolyte by a Rapid Charge/Discharge Circle, Journal of Physical Chemistry Letters 12 (2021) 2273-2278.

[4] K. Zhang, G. Zhou, , T. Fang, X. Tang, X. Liu, Different shapes based on ionic liquid leading to a two-stage discharge process, Journal of Materials Chemistry A 10 (2022) 7684-7693.