General and simple salts-mediating approach enables superior magnesium plating/stripping properties

Abstract

Rechargeable Mg-metal batteries represent attractive alternatives to Li-ion/Li-metal counterparts owing to resource sustainability, cost and safety superiorities. Grignard reagents-based electrolytes enable Mg plating/stripping reversibly, but properties are still not satisfactory. In this work, a general and simple salts-mediating approach is proposed to enrich electrochemically-active species in Grignard reagents-based electrolytes. This hybrid electrolyte exhibits high ionic conductivity of 19.47 mS cm⁻¹ (vs. 5.65 mS cm⁻¹ for pure electrolytes), desirable electrochemical window (2.75 V vs. 1.75 V for pure electrolytes), exceptional Mg plating/stripping properties (140 cycles vs. 40 cycles for pure electrolytes). After introducing magnesium bis(trifluoromethanesulfonimide)/diglyme (abbreviated as “Mg(TFSI)₂/G2”), originally negatively-charged ion pair species, such as [MgCl₃]⁻ and [Mg₂Cl₅]⁻, that adversely contribute to ionic conductivity and charge transfer processes, transform to active cations of [Mg(G2)₂]²⁺ and [MgCl]⁺ through Mg²⁺-assisted Mg-Cl bond dissociation. This greatly improves active ion accessibility for Mg-metal anode and is beneficial for uniform Mg electrodeposition. In addition, unique MgCl-rich and carbonyl organic compounds-containing interphases are unveiled, which is conducive to active Mg electrodeposition. This general and simple salts-mediating approach can be extended to design better electrolytes for next-generation multivalent-metal batteries.