Chelating Anion‐Mediated Solvation Structures for Rechargeable Magnesium Batteries

Abstract

ABSTRACT 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 (1 R ,2 R )‐1,2‐diphenylethane‐1,2‐diylbis(trifluoromethylsulfonylamide) (MgEDTF), featuring a chelating anion that modulates the solvation structure of Mg 2+ . 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 [Mg 2+ –(EDTF 2− )–(DME)] complex. Distinct from the conventional [Mg 2+ –(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 Mg 2+ solvation shell, forming an unsaturated [X − →Mg 2+ –(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.