S_8 reduction processes and Mg reactivity in a Mg-S_8 battery

Abstract

Mg batteries are an attractive next-generation energy storage option due to the high volumetric capacity of the Mg-metal anode compared to traditional Li-intercalation anodes such as graphite. Pairing the Mg anode with a S_8 cathode produces an economical cell from sustainable materials, however, designing electrolytes compatible with both Mg and S_8 is challenging. I will discuss my work detg. the effect of solvent on S_8 redn. in Mg-S batteries and passivation at the Mg anode. Prepg. Mg electrolytes with varied solvent systems is difficult due to the strong dependence of Mg^(2+) speciation on the solvent. To study the effect of solvent, the magnesium aluminum chloride complex (MACC) electrolyte was prepd. in various ethereal solvents. Reversible Mg electrodeposition and stripping was demonstrated in the MACC electrolyte and the electrodeposition overpotentials and current densities were found to vary with solvent. The S_8 redn. chem. was also found to be dependent on the electrolyte compn., suggesting solvent-mediated redn. pathways. The redn. products and redn. mechanisms are found to be different from the analogous Li-S system and begin to provide insight into the redox mechanisms of the Mg-S cell. Importantly, the reactivity of the Mg surface with the electrolytes is found to be of significant importance and methods to bypass this limitation will be presented.

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