On the role of electrolyte in aprotic MgO2 battery performance.

Being attractive among metal-air batteries due to its high theoretical energy density and voltage, aprotic magnesium-oxygen system is still much less studied than alkali metal-oxygen ones. Here we report a comparative study of Mg–O 2 cells with carbon-based cathode in various aprotic solvents: DMSO, diglyme, MeCN and tetramethylene sulfone. We found that the main discharge product in DMSO-based electrolyte is amorphous MgO 2 , with noticeable concentration of sulfur-containing byproducts being revealed. Upon partial electrode passivation, one-electron oxygen reduction to superoxide is observed on cycling voltammograms, and MgO 2 is predominantly formed by chemical disproportionation of superoxide. As for recharge, it was shown that the depassivation of the electrode proceeds along with the electrolyte (or carbon electrode) oxidation in any electrolyte solvents. In electrolyte solvents except DMSO the discharge capacity is quite limited due to metallic Mg anode issues. The addition of chloride ions to DMSO- and diglyme-based electrolyte solution increases the discharge voltage without affecting the charge process. The results contribute to the further development of electrolyte composition for rechargeable MgO 2 electrochemical system. [ABSTRACT FROM AUTHOR]