Magnesium perfluorinated pinacolatoborate in diglyme: understanding microscopic structures in rechargeable magnesium batteries

Abstract

Magnesium-ion batteries are a hot research topic, thanks to their arguable potential for rechargeable portable devices. Unlike lithium, magnesium is the eighth most abundant element in the Earth's crust, exhibiting physicochemical merits as an anode material. Thermodynamically and electrochemically stable electrolyte solutions must work in conjunction with Mg-ion batteries. We report a computational investigation of the recently synthesized chloride-free electrolyte, magnesium fluorinated pinacolatoborate [Mg][FPB]₂ in diglyme (DGM). [Mg][FPB]₂ exhibits a fascinating electrochemical performance, making it suitable for high-voltage Mg-ion batteries. By determining a representative manifold of low-energy stationary points in the [Mg][FPB]₂ and [Mg][FPB]₂ + DGM electrolyte compositions, we characterized non-covalent features and solvation shells, partial charge distributions, electrostatic potentials, electron transfers, solvation thermodynamics, nucleophilic and electrophilic binding centers, and other relevant properties. We found that DGM and FPB competed for the most thermodynamically favorable solvation of the Mg-ion. DGM readily penetrated the ion [Mg][FPB]₂ triplet and formed a few Mg⋯O ionic bonds. Competitive Mg⋯FPB and Mg⋯DGM bindings foster the mobility of a charge carrier in the electrolyte. The newly reported findings rationalize previous experimental observations and provide new predictions for electrochemists developing magnesium metal batteries.