Experimental and Molecular Insights into the Structure–Property Relationship of LiTFSI-Acetamide Eutectic Mixtures

Deep eutectic solvents (DESs) have been more frequently applied in electrochemical energy storage due to their favorable physicochemical properties. Acetamide and its methylated derivatives are promising solvents for forming DESs with lithium salts. In this work, three representative systems, combined by LiTFSI and acetamide/N-methylacetamide/N,N-dimethylacetamide, are selected to assess their structure–property relationship involved in the solid–liquid equilibria (SLE), density, viscosity, conductivity, and electrochemical stability window (ESW). The SLE of three systems is first experimentally measured to reveal their eutectic behavior, and thereafter, the other four properties are experimentally determined around the eutectic composition. Molecular dynamics simulations and quantum chemical calculations are performed to further investigate the microscopic properties of the mixtures. For the investigated systems, the coordination interaction, hydrogen-bonding interaction, and steric effect jointly affect the solvation structure of the electrolyte, leading to variations in these experimental properties. In the case of eutectic characteristics, density, viscosity, and conductivity, the relevant simulation results match the experimental data well; whereas, for the ESW, the microscopic analysis faces a challenge due to its association with chemical reaction pathways. These results provide a hybrid experimental and theoretical framework for identifying the structure–property relationship of DES systems, advancing rational electrolyte design.