The dynamic evaporation process of the deep eutectic solvent LiTf2N:N-methylacetamide at ambient temperature

Abstract

Lithium-based deep eutectic solvents (DESs) are potential and promising electrolytes for energy-storing devices such as the lithium-ion battery and supercapacitor due to their greenness, low cost, favorable stability, and ease of synthesis. LiTf₂N (lithium bis(trifluoromethylsulfonyl)imide):NMA (N-methylacetamide) is a liquid due to the strong intermolecular H-bonding interaction between the H-bonding acceptor (HBA, LiTf₂N) and H-bonding donor (HBD, NMA). The properties (melting point, conductivity, viscosity, etc.) of LiTf₂N:NMA change with the evaporation of NMA from LiTf₂N:NMA, which would further influence the performance of the energy-storing devices. The evaporation of DES should be determined by the intermolecular interactions. Here, for the first time, the dynamic process of evaporation and intermolecular interactions of the DES LiTf₂N:NMA at room temperature were investigated and we find that the evaporation mechanism of the DES LiTf₂N:NMA can be divided into three stages. In the first stage (before 110 min), the H-bonding interaction between O in LiTf₂N and NH in NMA is disrupted before destruction of the coordinating interaction related to amide II CO and Li cation. In the second stage (from 110 min to 270 min), the change of coordinating interaction related to amide II CO and Li cation is also higher than that of the H-bonded interaction. In the third stage (after 270 min), evaporation of NMA from LiTf₂N:NMA has very little influence on the environment of LiTf₂N:NMA. This work provides a guide for designing DESs as electrolytes for energy-storing devices such as the lithium-ion battery and supercapacitor.