Evaluation and realization of safer Mg-S battery: The decisive role of the electrolyte

Abstract

The magnesium–sulfur (Mg-S) battery may be a safer alternative for the lithium-sulfur battery because Mg plating usually proceeds without dendrite formation. Here, we correlate the thermal runaway of Mg-S battery with the associated change of electrolyte vapour pressure via battery testing calorimetry. Over-pressure builds up along with the programmed heating of the cell, and as a result, the thermal runaway is triggered at 20–45 K over the electrolyte boiling point, corresponding to 70–150 kPa pressure difference between the cell and the environment. The distinct performance-safety-cost behaviours of three ether type of electrolytes stems from the different CH 2 CH 2 O chain lengths. Such molecular insight will serve as a fundamental guideline in choosing and designing the desired electrolyte that simultaneously achieves a high explosion limit and good electrochemical performance . The safety of the MgS battery is mainly related to the vapour pressure of the electrolyte. The over-pressure builds up along with heating of the cell and triggers the battery explosion. The subsequent exothermic reaction between MgS and H 2 O caused a sudden temperature jump of the battery. A modified DME with higher boiling point will be ideal of the MgS battery. • A novel method of safety evaluation is introduced to the Mg-S system. • The thermal runaway of Mg-S battery is correlated with the associated change of electrolyte vapour pressure. • The distinct performance-safety-cost relationship of ether electrolytes with different degree of polymerisation.