Voltage hysteresis of magnesium anode: Taking magnesium-sulfur battery as an example

Abstract

Magnesium is considered one of the most promising anode materials. However, it is easy to react with electrolyte to form an ionic insulating passive film, causing a common phenomenon of voltage hysteresis and the resultant deteriorated electrochemical performance for magnesium batteries. Here, the voltage hysteresis of magnesium-sulfur batteries in Mg(ClO4)2 electrolyte is confirmed to be a consequence of magnesium passivation through three-electrode test and electrochemical impedance spectroscopy (EIS) measurements. The continuous competition relation between the formation and destruction of the passive film during magnesium stripping is discovered. The destruction process is controlled by the current density on magnesium anode, and the formation process is mainly affected by the concentration of anions causing passivation. Bromide ions as electrolyte additive can protect the magnesium surface from ClO4− anions and regulate the composition and thickness of the surface film, and the passivation of magnesium and the voltage hysteresis can be suppressed obviously. This work provides an important reference for further regulation of passivation behavior of magnesium anode.