Abstract

Deep eutectic solvents (DESs) represent a paradigm in green chemistry, where liquid solvents are prepared by mixing two solid precursors without any chemical reaction [1]. The resulting liquid arises from eutectic-type solid-liquid equilibrium. Recently, this DES framework was extended to the so-called deep eutectic electrolytes (DEEs), which incorporate an electrolyte component as one of the precursors [2]. Instead of dissolving a conventional solid electrolyte in an organic solvent, a solid salt (e.g., LiTFSI) is mixed with a compatible precursor to form a eutectic at room temperature. These DEEs combine the low cost, non-volatility, and environmental benignity of DESs with the high ionic mobility and electrochemical stability required for energy-related applications.

In this work, a combination of computational approaches, namely molecular dynamics and the thermodynamic model COSMO-RS, was employed to investigate the formation of DEEs. The main intermolecular interactions between DEE precursors were studied, enabling the formulation of heuristic rules to readily identify precursor pairs capable of forming liquid DEEs. Moreover, this work demonstrates how negative deviations from ideality can be reliably predicted and achieved, thereby facilitating DEE formation with severe melting point depressions. Finally, based on the developed predictive framework, several new DEEs with high interest for energy-related applications were proposed and experimentally validated.

Acknowledgements

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UID/50011/2025 (DOI 10.54499/UID/50011/2025) & LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020), financed by national funds through the FCT/MCTES (PIDDAC).

References

[1] D. O. Abranches and J. A. P. Coutinho. Annual Review of Chemical and Biomolecular Engineering 14 (2023): 141-163.

[2] Rui-Lan Liu, W. Yang, Q. Wang, X. Du, B. Hu, Y. Chen, and Dan-Yang Wang. Ceramics International 50, no. 5 (2024): 8178-8184.