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 4VC-Li+,4VC-Na+,4ES-Li+,4ES-Na+,4FEC-Li+,and 4FEC-Na+are the maximum thermodynamic stable solvation complexes.Besides,it is indicated that the innermost solvation shells are consisted of 5VC-Li+/Na+,5ES-Li+/Na+,and 5FEC-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 nVC-Li+/Na+and nFEC-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 nES-Li+/Na+solvation complexes moves to high frequency with the decrease of the Li+/Na+concentration,the S=O vibration in nES-Na+is higher than that in nES-Li+.The study is meaningful for the design of new-type Li/Na battery electrolytes.