Low-Cost Flame-Retardant Deep Eutectic Electrolytes for Sodium-Based Energy Storage: A Molecular-Level Study

High Resolution Image Download MS PowerPoint Slide Molecular-level understanding of the structural organization and transport behavior of deep eutectic electrolytes is key to the rational design of electrolytes for electrochemical applications with improved properties. Here, sodium-based deep eutectic electrolytes containing sodium nitrate and formamide were investigated using a combination of electronic structure calculations and classical molecular dynamics simulations, complemented by comparisons with experimental transport properties. Three electrolyte compositions were analyzed to evaluate the influence of solvent concentration on the microscopic structure and macroscopic transport behavior. The structural analysis reveals that the local organization of the electrolyte is governed by a competition between direct Na + –NO 3 – ion pairing and Lewis acid–base coordination between Na + and the carbonyl oxygen of formamide. Increasing the formamide content progressively replaces nitrate anions in the first solvation shell of Na +, leading to smaller aggregates and a more solvent-separated ionic environment. Consequently, the diffusion coefficients increase systematically with formamide concentration, whereas the viscosity decreases and the ionic conductivity increases slightly as a result of remaining ion correlations. The calculated conductivities are in excellent agreement with experimental measurements, indicating that the simulations capture the main structural and dynamical features of the electrolyte. These results highlight the key role of solvent coordination and ion-pair correlations in modulating both the microscopic structure and transport properties of sodium-based deep eutectic electrolytes.