Unique Behavior of Dimethoxyethane (DME)/Mg(N(SO₂CF₃)₂)₂ Solutions

Mg(N(SO₂CF₃)₂)₂ (MgTFSI₂) solutions with dimethoxyethane (DME) exhibit a peculiar behavior. Over a certain range of salt content, they form two immiscible phases of specific electrolyte concentrations. This behavior is unique, as both immiscible phases comprise the same constituents. Thus, this miscibility gap constitutes an exceptionally intriguing and interesting case for the study of such phenomena. We studied these systems from solutions structure perspective. The study included a wide variety of analytical tools including single-crystal X-ray diffraction, multinuclei NMR, and Raman spectroscopy coupled with density functional theory calculations. We rigorously determined the structure of the MgTFSI₂/DME solutions and developed a plausible theory to explain the two-phase formation phenomenon. We also determined the exchange energy of the "caging" DME molecules solvating the central magnesium ion. Additionally, by measuring the ions' diffusion coefficients, we suggest that the caged Mg²⁺ and TFSI^- move as free ions in the solution. Knowledge of the arrangement of the solvent/cation/anion structures in these solutions enables us to explain their properties. We believe that this study is important in a wide context of solutions chemistry and nonaqueous electrochemistry. Also, MgTFSI₂/DME solutions are investigated as promising electrolyte solutions for rechargeable magnesium batteries. This study may serve as an important basis for developing further MgTFSI₂/ether based solutions for such an interesting use.