Regulating the Electrochemical Performance of Simple Halogen-Free Electrolyte Using Ammonium Bromide Additive for Magnesium-Sulfur Battery Applications

Abstract

Magnesium-sulfur (Mg-S) batteries are a promising energy storage system; however, the short cycle life, low coulombic efficiency, and the shuttle effect of polysulfide hinder its practical application. Applying electrolyte additives is a powerful technique to optimize the electrochemical performance of Mg-S electrolytes. Herein, ammonium bromide (NH 4 Br) is used as an inorganic electrolyte additive in the halogen-free electrolyte (HFE) to guide homogeneous Mg deposition. It can be noticed that the addition of NH 4 Br decreases the activation energy values from 0.14 eV to 0.10 eV and reduces the value of Mg 2+ stripping/plating overpotential. It is found that the introduction of NH 4 Br to HFE enhances the cycle life and the initial discharge capacity (~1662 mAhg -1 ) of the Mg-S cells compared with the cells using free NH 4 Br that deliver initial discharge capacity of ~ 184 mAh g -1 , low coulombic efficiency, and short cycle life. Further efforts have been devoted by implementing a BaTiO 3 (BTO) as a modified separator to overcome the polysulfide dissolution issue in the cell. The surface of the cell's anode applying a modified separator shows half wt.% S content compared with the bare cell after cycling. This study opens further research for developing novel electrolyte schemes for magnesium-sulfur battery applications.