Nonflammable Ether and Phosphate-Based Liquid Electrolytes for Sodium-Ion Batteries

This study investigates a group of electrolytes containing NaPF₆ or NaBF₄ salts in phosphate- and ether-based solvents for high-mass loading sodium-ion batteries. It explores physicochemical properties such as ionic conductivity, dynamic viscosities, and nonflammability. The combination of experimental with computational studies reveals detailed insights into the physicochemical properties of the nonflammable liquid electrolytes. Diglyme-based electrolytes become nonflammable with 50 vol % phosphate solvents, while tetraglyme-based electrolytes require 70 vol %. The solvation structure has been investigated using NMR and is combined with computational studies to provide information about properties such as solvation structure, ionic conductivity, and viscosity. The molecular dynamic simulations confirm the enhanced solvation in diglyme-based liquid electrolytes observed experimentally by ²³Na-NMR. Despite lacking sufficient electrochemical stability, this work provides a fundamental understanding of the solvation structure and physicochemical properties of a novel electrolyte system. This is an important contribution to be applied in future electrolyte design rationale.