Anion effects on the solvation structure and properties of imide lithium salt-based electrolytes

The anion effect on Li⁺ solvation structure and consequent electrochemical and physical properties was studied on the basis of LiFSI-DMC (lithium bisfluorosulfonyl imide-dimethyl carbonate)- and LiTFSI-DMC (lithium bis(trifluoromethanesulfonyl imide)-dimethyl carbonate)-based dilute electrolytes, highly concentrated electrolytes, and localized concentrated electrolytes. With different anions, the electrolytes are different in possible solvation structures and charge distributions, leading to differences in terms of thermal properties, viscosity, ionic conductivity, electrochemical oxidation and reduction behaviors as well as LiNi_0.6Mn_0.2Co_0.2|Li cell performances. The results indicate that the electronic structure of anions contributes greatly to the charge distribution of the Li⁺ solvation sheath, and consequently extends to the thermodynamics of the carbonate molecules, affecting reduction, oxidation reaction and products on the interface between electrolytes and electrodes. The comprehensive understanding of the solution structure and properties is necessary for the rational design of advanced electrolytes.