Most magnesium electrolytes react with the Mg anode surface to form a non-favorable passive layer that inhibits shuttling of the Mg ions and results in the short cycle life of the Mg cells. In this work, we probe LiF as an effective electrolyte additive to address the challenges of electrolyte degradation, Mg anode passivation, and polysulfide shuttle. The key to our strategy lies in modifying the halogen-free electrolytes (HFE) electrolyte-based Mg(NO3)2·6H2O salt dissolved in acetonitrile (ACN) and tetra ethylene glycol dimethyl ether (G4) with LiF additives, which play a crucial role in engineering stable electrolyte interfaces. These additives alter the chemical composition of the solid electrolyte interface (SEI) layer on the surface of the Mg anode, enabling low overpotential of Mg2+ extraction/insertion, improving the Mg2+ transference, and enhancing the electrochemical performance of the electrolyte. The Mg-S cell with modified electrolyte delivers a high discharge capacity of over 400 mAh g−1 for >10 cycles, compared with the short cycle life in the case of using a blank electrolyte. This remarkable performance underscores the potential of our findings in advancing magnesium sulfur battery technology.