Understanding solvation-properties relationships is crucial for developing battery electrolytes. Using molecular design, molecular simulation, and electrochemical characterization, we systematically investigate the solvation structure, transport property, and electrochemical stability of a new family of fluorinated ether solvents. First, our molecular simulations predict that properties such as solubility, conductivity, and oxidative stability of the fluorinated solvent are sensitive to the length of the ethereal segment and fluorocarbon segment. Specifically, a longer ethereal segment better dissolves salt and suppresses the formation of ionic aggregates, which helps increase the ionic conductivity of the electrolytes. Meanwhile, the longer fluorocarbon segment improves oxidative stability but impairs ionic conductivity. Next, solvents predicted to be promising candidates by our computational studies were synthesized and evaluated as electrolyte solvents for Li metal batteries. In combination with lithium bis(trifluoromethanesulfonyl)imide salt, the fluorinated ether-based electrolytes exhibit significantly improved capacity retention and higher Coulombic efficiency during aging cycling compared to baseline electrolytes. This work demonstrates a prolific approach to the rational design of novel electrolytes through tailoring the chemical structures to modify solvation structures and improve the physicochemical properties.

Fluorinated ether solvents for Li metal batteries

ACS Fall 2021

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