Enhancement of the discharge behavior for Mg-air battery by adjusting the chelate ability of ionic liquid electrolyte additives

Abstract

Mg-air primary battery is an important energy source with the distinct merits. However, in practical terms, both the utilization efficiency and the cell voltage are much less than the corresponding theoretical values due to the serious self-corrosion and fast anode fouling. Variation of chemical composition of Mg anode is a feasible pathway to refine the discharge performance, but it is only suitable for one specific anode. Involvement of additives in electrolytes is an alternative strategy that is possible suitable for various anodes. Three ionic liquids, choline glycolate ([Ch][GA]), choline salicylate ([Ch][SAL]), and choline 8-hydroxyquinoline-5-sulfonate ([Ch][HQSA]), are synthesized and firstly utilized as the electrolyte additives for Mg-air primary battery. The discharge performance is determined by half-cell and full-cell discharge measurements. The highest specific energy for Mg-air battery based high-purity Mg anode (Hp-Mg) is 2180.18 Wh kg−1 with 0.1 M [Ch][SAL] under 2.5 mA cm−2. The excellent performance of [Ch][SAL] is attributed to the cooperation of several items, in which the [SAL]− anion could chelate the Mg2+ ions to form the soluble Mg-complex, and the [Ch]+ could suppress the self-corrosion of Mg anode and hydrogen evolution. The inferior behavior of [Ch][GA] and [Ch][HQSA] is attributed to the weak or strong chelate ability of [GA]− and [HQSA]− anion toward Mg2+ ions. More importantly, the addition of [Ch][SAL] is also suitable for Mg-air primary battery based on AM50, AZ31, and ZK61 anodes. Development of electrolyte additives with various functions is an efficient pathway to refine the discharge performance of Mg-air cell.