Reversible function switching of Ag catalyst in Mg/S battery with chloride-containing electrolyte

Rechargeable Mg/S batteries suffer from fast capacity decay because of the difficult re-oxidation of MgS. To tackle this problem, we used Ag catalyst in Mg/S cells with Cl- containing electrolyte, and achieved a greatly improved specific capacity of similar to 1200 mAh.g(-1) and a long cycling life of 100 cycles. To understand the mechanism behind this improvement, we employed in-situ synchrotron radiation X-ray diffraction and in-situ X-ray absorption spectroscopy tools to study the reversible phase transitions during charge/discharge cycling. The in-situ experiment results revealed that, at deeply charged state, Ag reacted with Cl- in the electrolyte to form the AgCl interfacial layer which prevented the physical contact of Ag with elemental S and avoided the formation of Ag2S; at early discharged state, AgCl transformed back to metallic Ag, which guaranteed its catalytic effectiveness for MgS decomposition. This reversible function switching mechanism of Ag catalyst is completely different from that in Mg/S cells using other catalysts or electrolytes.

Automated summary

By using Ag catalyst and Cl- containing electrolyte in Mg/S cells, the specific capacity and cycling life can be greatly improved. Experimental results reveal a reversible function switching mechanism of Ag catalyst in charge/discharge cycling.