A Simple Cl^--Free Electrolyte Based on Magnesium Nitrate for Magnesium-Sulfur Battery Applications

The magnesium-sulfur (MgS) battery is a promising alternative to the post-lithium battery because of its low-cost construction, eco-friendliness, high theoretical energy density, and safety. However, the lack of simple compatible electrolytes, self-discharge, polysulfide shuttle effect, and the slow conversion reaction pathway still limit its practical applications. Here, we propose a simple halogen-free electrolyte (HFE) based on Mg(NO₃)₂ dissolved in the cosolvent of acetonitrile (ACN) and tetraethylene glycol dimethyl (G4) that applies to a Mg/S full cell. The as-prepared Mg-ion electrolyte exhibits efficient Mg plating/stripping performance, high anodic stability (vs Mg/Mg²⁺), and a high ionic conductivity of ∼10^-4 S cm^-1 at 313 K. Chronoamperometry (CA), scanning electron microscopy, and energy-dispersive spectroscopy examinations report that the HFE supports flat, dendrite-free, and translucent Mg deposits. Polymer layer interface (PLI)-based polyvinylidene fluoride (PVDF) and Mg(O₃SCF₃)₂ have been designed to isolate the surface of the Mg anode from the liquid electrolyte. A sulfur cathode with the anchoring materials of silicon carbide and barium titanate-based material has been designed and characterized. The Mg/S battery has been constructed with an initial discharge capacity of up to 1200 mAh g^-1, and it has retained a reversible capacity at 100 mAh g^-1 after 10 cycles. This study offers a pivotal role in designing a promising HFE candidate for a high-performance MgS battery.