Mg batteries are a promising energy storage system because of physicochemical merits of Mg metal as an anode material. However, the lack of electrochemically and chemically stable magnesium electrolytes impedes the development of Mg batteries. In this study, a newly designed chloride-free magnesium fluorinated pinacolatoborate, Mg[B((CF3)4C2O2)2]2(abbreviated as Mg-FPB), was synthesized by convenient methods from commercially available reagents and fully characterized. The Mg-FPBelectrolyte delivered outstanding electrochemical performance, specifically, 95% coulombic efficiency and 197 mV overpotential for reversible Mg deposition, and anodic stability up to 4.0 V vs Mg. The Mg-FPBelectrolyte was applied to demonstrate a high voltage rechargeable Mg/MnO2battery with a discharge capacity of 150 mAh/g.