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

Abstract Reversible magnesium (Mg) plating/stripping is a key challenge for Mg metal batteries. Hence, a dual‐functional additive, tin(II) fluoride (SnF ₂ ), 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 SnF ₂ 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 Mg ²⁺ . Concurrently, the competitive coordination of F ⁻ anions from SnF ₂ 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.