Dual-Functional Electrolyte Additives to Enhance Magnesium Plating/Stripping Performance for Rechargeable Magnesium Metal Batteries With Pure Amine Solvents

Reversible magnesium (Mg) plating/stripping is a key challenge for Mg metal batteries. Hence, a dual-functional additive, tin(II) fluoride (SnF₂), is introduced into the simple Mg salts (Mg(OTf)₂ and Mg(TFSI)₂) electrolytes with a pure amine solvent (3-methoxypropylamine, MOPA). Interfacial characterizations and theoretical calculations reveal that the dissociated SnF₂ can drive the in-situ formation of a multiphase Sn-based solid-electrolyte interphase (SEI) on the Mg anode. Such a robust and magnesiophilic SEI shields the Mg metal from MOPA-induced corrosion and parasitic reaction, while facilitates the interfacial kinetics of Mg²⁺. Concurrently, the competitive coordination of F⁻ anions from SnF₂ raises the contact ion pairs and further mitigates the MOPA decomposition. As a result, the reversibility of Mg metal anode is successfully enhanced, and Mg//Cu cells maintain over 1000 cycles at 2.0 mA cm⁻² with an average Coulombic efficiency exceeding 99.8%. This work offering a promising pathway toward practical application of high-performance Mg metal batteries.