DFT study of solvation of Li~+/Na~+ in fluoroethylene carbonate/vinylene carbonate/ethylene sulfite solvents for lithium/sodium-based battery

Choosing suitable solvent is the key technology for the electrochemical performance of energy storage device. Among them, vinylene carbonate(VC), fluoroethylene carbonate(FEC), and ethylene sulfite(ES) are the potential organic electrolyte solvents for lithium/sodium battery. However, the quantitative relation and the specific mechanism of these solvents are currently unclear. In this work, density functional theory(DFT) method is employed to study the lithium/sodium ion solvation in solvents of VC, ES, and FEC. We first find that 4 VC-Li~+, 4 VC-Na~+, 4 ES-Li~+, 4 ES-Na~+, 4 FEC-Li~+, and4 FEC-Na~+are the maximum thermodynamic stable solvation complexes. Besides, it is indicated that the innermost solvation shells are consisted of 5 VC-Li~+/Na~+, 5 ES-Li~+/Na~+, and 5 FEC-Li~+/Na~+. It is also indicated that the Li~+solvation complexes are more stable than Na~+complexes. Moreover, infrared and Raman spectrum analysis indicates that the stretching vibration of O = C peak evidently shifts to high frequency with the Li~+/Na~+concentration reducing in n VC-Li~+/Na~+and n FEC-Li~+/Na~+solvation complexes, and the O = C vibration peak frequency in Na~+solvation complexes is higher than that of Li~+complexes. The S = O stretching vibration in n ES-Li~+/Na~+solvation complexes moves to high frequency with the decrease of the Li~+/Na~+concentration, the S = O vibration in n ES-Na~+is higher than that in n ES-Li~+. The study is meaningful for the design of new-type Li/Na battery electrolytes.