Influence of cations in lithium and magnesium polysulphide solutions: dependence of the solvent chemistry

In order to gain a deeper understanding of Li and Mg polysulphides in Li/S and Mg/S batteries, respectively, this work investigates the impact of the two different cations as well as the influence of the electrolyte solvents' relative dielectric permittivity and Gutmann's donor number on the solubility and relative stability of different Li and Mg polysulphide species. Therefore, the disproportionation and dissociation equilibria of chemically prepared “Li2S8” and “MgS8” solutions in DMSO, DMF, ACN, THF, DME, TEGDME, and Pyr14TFSI are characterized by UV/Vis spectroscopy. Varying the cation and the solvent reveals their mutual interplay in stabilizing different polysulphide species. To our knowledge, this is the first time that chemically synthesized Mg polysulphides in solutions are studied. The results of this work provide essential knowledge for further development of the economically, ecologically, and also in terms of energy density and safety, attractive Mg/S batteries.