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

Abstract

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.

Solvent Effects on the Reversible Intercalation of Magnesium‐Ions into V2O5 Electrodes

“…The most important peak in this region is the one at 875 cm −1 . This peak is associated with the symmetric breathing mode of the three DME molecules encaging Mg 2+ ions in DME based solutions . This peak is observed even at relatively low concentrations of 1.5 M DME in 0.5 M Mg(ClO 4 ) 2 /ACN solution.…”

“…This spectral region is presented in Figure . The peak at 820 cm −1 is attributed to TTG conformers of free DME in the DME containing electrolyte solutions (822 cm −1 in pure DME) . The most important peak in this region is the one at 875 cm −1 .…”

Fervent Hype behind Magnesium Batteries: An Open Call to Synthetic Chemists—Electrolytes and Cathodes Needed

“…[58] Thee lectrochemical performance of Mg-(TFSI) 2 can be improved by the addition of MgCl 2 which is shown to increase both the current density and the coulombic efficiency of reversible magnesium deposition as the fraction of the magnesium chloride increases.H owever,t he addition of this magnesium chloride will presumably render this electrolyte corrosive in nature. [59][60][61] Interestingly,magnesium hexafluorophosphate dissolved in THF/CH 3 CN undergoes reversible magnesium deposition/stripping.H owever, the coulombic efficiencyi se xtremely low,s imilar to Mg-(TFSI) 2 . [62] Theo verpotential value negatively affects the energy density in abattery by lowering the discharge battery voltage and increasing the charging voltage.A ssuming am agnesium battery would discharge at 2.5 Vand charge at 3V with zero overpotential, the same battery would have adischarge voltage of 1Vand charge at 5Vif the electrolyte has an overpotential of 2Vat the operating current density.…”

Magnesiumbatterien – ein Aufruf an Synthesechemiker: Elektrolyte und Kathoden dringend gesucht

“…[56] Magnesiumorganoborate mit einem Magnesium-Dimer-Kation (Mg 2 (m-Cl) 3 ·6 THF) + zeigten hingegen auf Platin sowie auf Edelstahl und Aluminium ähnliche oxidative Stabilitäten. [59][60][61] Interessanterweise unterliegt in THF/CH 3 CN aufgelçstes Magnesiumhexafluorphosphat einer reversiblen Abscheidung/Ablçsung von Magnesium, und wie bei Mg(TFSI) 2 ist der Coulomb-Wirkungsgrad extrem niedrig. Hervorzuheben ist, dass die Dimer-Kationen der Magnesiumorganohalogenaluminate und Magnesiumorganoborate korrosive Chloride enthalten.…”

“…Die elektrochemische Leistung von Mg(TFSI) 2 kann durch die Zugabe von MgCl 2 verbessert werden, und die Stromdichte sowie der Coulomb-Wirkungsgrad der reversiblen Magnesiumabscheidung erhçhen sich mit steigendem Magnesiumchlorid-Anteil. Vermutlich macht die Magnesiumchlorid-Zugabe den Elektrolyten jedoch korrosiv [59][60][61]. Interessanterweise unterliegt in THF/CH 3 CN aufgelçstes Magnesiumhexafluorphosphat einer reversiblen Abscheidung/Ablçsung von Magnesium, und wie bei Mg(TFSI) 2 ist der Coulomb-Wirkungsgrad extrem niedrig.…”