Novel dual-function electrolyte additive for high-power aqueous Mg-air battery: Improvement of both discharge potential and utilization efficiency

Abstract

A novel ionic liquid, choline 2,6-dihydroxytbenzoate ([Ch][DHB]), is firstly synthesized and utilized as the electrolyte additive for aqueous Mg-air cell based on the high purity Mg (Hp-Mg) with the aim to enhance the discharge performance. The half-cell discharge test, electrochemical measurement, and real-time hydrogen evolution are carried out to evaluate the influence of [Ch][DHB] and clarify the working mechanism. The [DHB]- anion could bind the Mg2+ ions to form the complex, which is beneficial to prompt the discharge of Mg matrix; while the [Ch]+ cation is effective to inhibit the self-corrosion of Mg anode. With the addition of 0.2 M [Ch][DHB] in the 3.5 wt% NaCl, both discharge potential and utilization efficiency are enhanced to −1.64 VSCE and 68.0 % under 5 mA cm−2. Based on the above Mg-air cell, 66 of LED bulbs (0.04 W/per bulb) would be maintained for 132 h with 0.2 M [Ch][DHB] in the electrolyte, while they are only kept for 65 h in the reference electrolyte. The 0.2 M [Ch][DHB] is also suitable electrolyte additives for Mg-air battery based on other commercial Mg anodes (AM50, AZ31, and ZK61). The specific energy of Mg-air batteries based on Hp-Mg, AM50, AZ31, and ZK61 in 0.2 M [Ch][DHB] electrolyte are 2093 Wh kg−1, 1788 Wh kg−1, 1896 Wh kg−1, and 713 Wh kg−1 at 5 mA cm−2, respectively. This work exhibits a promising pathway to enhance the discharge performance of Mg-air primary battery, including both discharge potential and utilization efficiency, with ionic liquids as electrolyte additives.