Improving the discharge performance of aqueous Mg-air battery using dicarboxylic acid additives

The aqueous Mg-air battery has promising applications in energy storage system. To improve the discharge performance of the Mg anode, four dicarboxylic acids including oxalic acid, malic acid, succinic acid, adipic acid are used as electrolyte additive for the aqueous Mg-air battery. The influence of the four selected additives and their reaction mechanism are systematically investigated by hydrogen evolution, electrochemical experiments (OCP, half/full-cell test, EIS), SEM, XRD, XPS and DFT calculations. The experiment results demonstrate that the dicarboxylic acid electrolyte additive can active the Mg anode evidently by increasing the hydrogen evolution volume and negative shift of discharge potentials. The surface morphology and the chemical composition analyses demonstrate that the four selected additives can form soluble complexes with Mg²⁺. The oxalic acid is the best electrolyte additive among the four dicarboxylic acids. The chelating ability of the additives and the pH of the electrolyte both affect the discharge performance of the Mg anode. The mechanism by which the dicarboxylic acids additives improve the discharge performance of the Mg anode is further proved by DFT calculations. It is the soluble Mg²⁺ complex (MgL, L: dicarboxylate) formed between the additives and the Mg anode that inhibit the formation of the corrosion products and promote the dissolution of the Mg anode, thus enhance the discharge performance of the Mg anode.