Tailoring the discharge performance of aqueous Mg-air batteries by salicylate derivatives

Aqueous Mg-air batteries (MABs) are promising for the high-energy-density storage but suffer from severe self-corrosion of the Mg anodes and the discharge suppression due to the formation of oxide products. Tailoring electrolyte additives is deemed as a critical means to address these limitations. Herein, salicylate derivatives with different functional groups (hydroxyl, thiol, sulfonic, methyl) were systematically investigated through half-cell discharge characterizations combined with density functional theory (DFT)/molecular dynamics (MD) simulations. The results show that the discharge performance of Mg-air is promoted by the addition of 0.1 M SA, 5-SSA, TA and 2,6-DHB, but significantly reduced impeded by 3-MSA. Both experimental and DFT/MD results indicate that the presence of hydroxyl/thiol/sulfonic groups within SA molecule provides additional sites for its complexation with Mg ions suppressing the precipitation of hydroxides on the Mg anode surface, whereas the methyl group helps the adsorption of 3-MSA on the corroding Mg surface. This work suggests that the category and position of the functional group play critical roles in determining the effect of the electrolyte additive for Mg-air battery.