Calcium and Magnesium Ions in Glyme and Ether Sulfone-Based Electrolytes: Insights into Solvation Structure and Dynamics

Abstract

Energy-storage devices based on Ca²⁺ and Mg²⁺ ions are promising alternatives for moving beyond lithium-ion batteries. The design of novel electrolytes for divalent metal ions requires a detailed knowledge of the coordination environment and ion transport. In this regard, glymes and ether sulfones form various multidentate solvation complexes with metal ions in electrolytes, promoting reversible electrodeposition of Ca²⁺ and Mg²⁺ by displacing the coordinating anion, while offering good electrochemical stability. To provide insights into the structural and dynamic properties of a wide variety of glyme and ether-sulfone electrolytes with Ca²⁺ and Mg²⁺ salts, we used molecular dynamic simulations with an extended CL&Pol polarizable force field, which is based on a fragment approach and is transferable to many families of molecules. Our simulation results show the dependence of the cation solvation environment structure on the choice of metal ion and salt anion in both classes of solvents, and reveal the interplay between the coordination of the metal ion by the ether and sulfonyl oxygens in ether sulfones. Additionally, we examine the impact of the solvent and additives on electrolyte viscosity and conductivity.