Ion–solvent chemistry in lithium battery electrolytes: From mono-solvent to multi-solvent complexes

Abstract

The building of safe and high energy-density lithium batteries is strongly dependent on the electrochemical performance of working electrolytes, in which ion–solvent interactions play a vital role. Herein, the ion–solvent chemistry is developed from mono-solvent to multi-solvent complexes to probe the solvation structure and the redox stability of practical electrolytes. The decrease in energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of solvents in lithium-ion solvation shells becomes less significant as the number of coordinated solvents increases, but both the HOMO and LUMO energies of the coordinated solvents remain lower than those of free solvents. A positive and approximately linear relationship was found between the decrease in the HOMO/LUMO energy and the average binding energy between Li+ and the coordinated solvents. A binary-solvent complex model further highlight the significant importance of the electrolyte solvation environment in regulating electrolyte stability, and it is essential to consider electrolyte stability from the perspective of ion–solvent complexes. These fresh insights into the energy chemistry of multi-solvent complexes provide critical references for electrolyte design and cell optimization.