Computational Insights into Mg‐Cl Complex Electrolytes for Rechargeable Magnesium Batteries

Abstract

DFT calculations were conducted to provide unprecedented thermodynamic insights on tetrahydrofuran (THF) solvation, isomerization, and complexation of possible MgÀ Cl coordination species for popular MgÀ Cl electrolytes for magnesium batteries. Computational results using the M06-2x functional with the 6-31 + G(d) basis set indicate that trigonal bipyramidal e,e-cis-tbp-MgCl 2 (THF) 3 dichloride species and octahedral [MgCl (THF) 5 ] + monochloride species are the dominant mononuclear species. These two can combine to form the dinuclear species [(μ-Cl) 3 Mg 2 (THF) 6 ] + with a free energy À 6.30 kcal/mol, which is calculated to be the dominant MgÀ Cl species in solution. Two mono-cation species, [(μ-Cl) 3 Mg 2 (THF) 6 ] + and [MgCl(THF) 5 ] + , have comparable LUMO energies, thus both of them can act as active species for Mg deposition. However, the significant dominance of the dinuclear species in the electrolyte indicates that it is the primary species involved in reversible Mg deposition.[a] J.

Halide‐Based Materials and Chemistry for Rechargeable Batteries

“…Adetailed picture of the coordination chemistry of Mg-Cl complexes in the [Mg 2 (m-Cl) 3 ·6 THF] + electrolyte was recently presented by Moss et al using DFT calculations. [192] This study demonstrated that both [Mg 2 (m-Cl) 3 Similar high Mg/Al ratios in the conditioned MACC electrolyte could be directly obtained by an interesting method involving the catalytic dissolution of Mg into THF through the addition of as mall amount of CrCl 3 . [193] Consequently,the conditioning process is unnecessary.However, the conditioned MACC in THF with an anodic stability of 3.1 Vv ersus Mg and ah igh Mg/Al ratio suffered ad eterioration in performance when the electrolyte was allowed to rest under an inert atmosphere for one week (aging process).…”

“…A detailed picture of the coordination chemistry of Mg‐Cl complexes in the [Mg 2 (μ‐Cl) 3 ⋅6 THF] + electrolyte was recently presented by Moss et al. using DFT calculations . This study demonstrated that both [Mg 2 (μ‐Cl) 3 ⋅6 THF] + and [MgCl(THF) 5 ] + monocations can act as active species for Mg deposition, with the dominant active species being the [Mg 2 (μ‐Cl) 3 ⋅6 THF] + dimer.…”

Structure of Magnesium Chloride Complexes in Ethereal Systems: Computational Comparison of THF and Glymes as Solvents for Magnesium Battery Electrolytes

“…Here, our goal is to provide thermodynamic insight on the solvation, isomerization, and complexation of possible MgÀ Cl species in ethereal solvents based on DFT calculations. The structure of THF-based electrolytes has been thoroughly studied before, [27,28] and provides a good starting point for exploring different glycol ethers, which are more suitable for battery application, due to their higher thermal and chemical stabilities. Such a detailed understanding of the solvation behavior is a prerequisite for developing high-performance electrolytes for magnesium batteries, finally showing how distinct structures formed in diglyme (G2) can enhance the processes at the electrodes.…”

Halogenid‐basierte Materialien und Chemie für wiederaufladbare Batterien

“…vorgestellt. Dazu wurden DFT‐Rechnungen verwendet, welche veranschaulichten, dass sowohl [Mg 2 (μ‐Cl) 3 ⋅6 THF] + ‐ als auch [MgCl(THF) 5 ] + ‐Monokationen als aktive Spezies für die Mg‐Abscheidung fungieren können, wobei die dominante aktive Spezies das [Mg 2 (μ‐Cl) 3 ⋅6 THF] + ‐Dimer ist.…”

“…Ein detailliertes Bild der Koordinationschemie der Mg-Cl-Komplexe im [Mg 2 (m-Cl) 3 ·6 THF] + -wurde kürzlich von Moss et al vorgestellt. Dazu wurden DFT-Rechnungen verwendet,[192] welche veranschaulichten, dass sowohl [Mg 2 (m-Cl)3 ·6 THF] + -a ls auch [MgCl(THF) 5 ] + -Monokationen als aktive Spezies fürdie Mg-Abscheidung fungieren kçnnen, wobei die dominante aktive Spezies das [Mg 2 (m-Cl) 3 ·6 THF] + -Dimer ist. Ein ähnlich hohes Mg:Al-Verhältnis in dem konditionierten MACC-Elektrolyten konnte direkt durch Ausführung einer interessanten Methode erreicht werden, welche die katalytische Auflçsung von Mg in THF durch die Zugabe einer kleinen Menge von CrCl 3 beinhaltet.…”