Synthesis and Electrochemical Properties of Organic Gel Electrolytes Based on Low Molecular Weight Gelators
Authors: Matsumoto Kenta , Sugiura Takumi , Suzuki Nonoka , Morita Yuki , Okamoto Hiroaki 
Published: December 2024

Introduction

Several low molecular weight organic gelators (LMOGs) which are able to produce thermo-reversible gels (i.e., physical gels) with organic solvents have been discovered, and the gels are of great attentions for their application to organic gel electrolytes of Li-ion battery, dye-sensitized solar cells and so on [1]. These molecules create fibrous aggregates by self-assembly through non-covalent intermolecular interactions then they trap the solution, resulting in gelation.
In our previous papers, LMOG having perfluoroalkyl groups in the molecules can gelate aprotic polar solvents such as propylene carbonate (PC), γ-butyrolactone (GBL) and so on [2]. However, the correlation between LMOGs and the electrochemical properties of gel electrolytes formed using them has not been elucidated.
Here, we report preparation of LMOGs and thermal and electrochemical properties of the Li-ion gel electrolytes.

Experimental

Preparation of gels and determination of the sol-gel temperatures are as follows: Weighed amounts of a liquid and LMOG were placed into a glass tube (10 mmφ). The tubes were heated until all solid material had dissolved and then cooled. The transition temperatures were determined by the inverse flow method.
Linear sweep voltammetry (LSV) measurements for Li-ion electrolyte solution and the gel electrolyte were carried out in a potential range of 0–7 V vs Li/Li+ (≈ -3–4 V vs Ag/Ag+) at a rate of 1.0 mV s-1, where a pair of platinum were used as working and counter electrodes, and a silver wire was used as a reference then the potential converted to the appropriate values. The electrolyte solution was a 1M LiPF6/the mixture of ethylene carbonate and ethyl methyl carbonate (EC:EMC = 1:2 and/or 3:7). Cyclic voltammetry (CV) was carried out in a potential range of 0–3 V vs Li/Li at a rate of 1.0 mV s-1, where natural spheroidal graphite purchased from Hosen Co. Ltd. was used as a working electrode, and a pair of lithium metals were used as counter and reference electrodes.

Results and Discussion

The sol-gel transition temperature for gel electrolyte was found to be a function of the concentration of LMOG, where the concentration of LMOG increases, the transition temperature also increases. The transition temperatures also depend on the chemical structure of the LMOG and were approximately 30 ºC to 50 ºC at a concentration of about 5% of LMOG.
The results of LSV measurements of the Li-ion electrolyte and the gel electrolyte prepared by the addition of LMOG were very similar, indicating that the LMOG shows high electrochemical stability. The CV results indicate that the presence of the LMOG in the electrolyte solution is similar to the neat electrolyte solution on cycling behavior.
In this presentation, the preparation of the LMOGs, and thermal and electrochemical properties of the gel electrolyte will be discussed in terms of the chemical structure of the LMOGs.

Acknowledgements

This work is financially supported by JST SPRING [JPMJSP2111] and YAMAGUCHI UNIVERSITY FUND (to K.M.), JSPS KAKENHI [22H03781, 23K25035], Paloma environmental technology development foundation, Hoso Bunka Foundation, Japan Keirin Autorace Foundation and Iketani Science and Technology Foundation (to H.O.).

Reference

[1] L. Tao, et al., J. Mater. Chem. A, 3, 2344 (2015).
[2] T. Yoshida, et al., Bull. Chem. Soc. Jpn, 88, 1447 (2015), A. Ohashi, et al., Chem. Lett., 47, 810 (2018).

Figure 1