Interfacial processes of Mg anodes for magnesium-sulfur batteries: An EIS study

Abstract

The development of magnesium batteries strongly relies on the use of a Mg metal anode and its benefits of high volumetric capacity, reduction potential, low cost and improved safety, however, to date, it still lacks sufficient cycling stability and reversibility. Along with the electrolyte selection, the interfacial processes can be affected by the anode itself applying electrode engineering strategies. In this study, six different Mg anode approaches – namely bare Mg metal, Mg foil with an organic and inorganic artificial solid electrolyte interphase, Mg alloy, Mg pellet and a tape-casted Mg slurry – are selected to be investigated by means of electrochemical impedance spectroscopy in Mg|Mg and Mg|S cells. While a plating/stripping overpotential asymmetry was observed and assigned to the desolvation during Mg plating, the impedance spectra of stripping and plating hardly differ for all applied anodes. In contrast, the sulfur species significantly influence the impedance response by altering the surface layer composition. By systematic process assignment of the gained spectra in Mg|Mg and Mg|S cells, specific equivalent circuit models for different anodes and cell conditions are derived. Overall, the study aims to give valuable insights into the interfacial processes of Mg anodes to support their further development toward long-lasting Mg batteries.