Chelating Anion-Mediated Solvation Structures for Rechargeable Magnesium Batteries

Modifying solvents and additives to regulate cation solvation structures in electrolytes is a conventional approach, but the selection of solvents and additives suitable for rechargeable magnesium metal batteries remains limited. This study proposes a magnesium salt, magnesium (1R,2R)-1,2-diphenylethane-1,2-diylbis(trifluoromethylsulfonylamide) (MgEDTF), featuring a chelating anion that modulates the solvation structure of Mg²⁺. Compared to the non-chelating magnesium benzyl((trifluoromethyl)sulfonyl)amide (Mg(BnNTf)₂) analogue, the chelating anion of MgEDTF in 1,2-dimethoxyethane (DME) enters the primary solvation shell to form an unsaturated [Mg²⁺-(EDTF^2-)-(DME)] complex. Distinct from the conventional [Mg²⁺-(3DME)] structure, this configuration facilitates the formation of an anion-derived solid electrolyte interphase (SEI), thereby significantly reducing the Mg plating/stripping overpotential from 2.0 to 0.24 V. Moreover, trace halide additives synergize with the EDTF^2- anions to partially reconstruct the Mg²⁺ solvation shell, forming an unsaturated [X^-→Mg²⁺-(EDTF^2-)-(½DME)] (X^- = Cl^-, Br^-) structure. This configuration facilitates the formation of a more effective SEI by suppressing solvent decomposition, thereby further reducing the overpotential to below 0.20 V. This study demonstrates the feasibility of chelating anion-mediated solvation in rechargeable magnesium metal batteries and provides a novel approach for solvation structure modulation in other metal-based battery systems.