Electrochemical performance and discharge mechanism of Mg Sr binary alloys as anodes for Mg-air batteries

Owing to their high theoretical energy density and environmental friendliness, magnesium-air batteries are regarded as a highly promising novel energy source. However, their practical application is impeded by the severe self-corrosion and “chunk effect” of the magnesium anode. The development of new magnesium anodes is an effective approach to address these issues. Nevertheless, binary magnesium alloys composed of non-precious metal elements and fabricated via a simple melting process often fail to achieve satisfactory performance. In this study, we systematically investigated the discharge performance of three as-cast Mg-xSr (x = 0.1, 0.5, and 1 wt%) binary alloys as anodes for magnesium-air batteries. The results demonstrated that the Mg-0.1Sr alloy exhibited the best discharge performance, with the highest anode utilization efficiency (60.6 %), specific capacity (1336.3 mAh g −1 ), and specific energy (1872.1 Wh kg −1 ). These superior properties can be attributed to refined grain size of the magnesium matrix, mitigation of “chunk effect”, and effective suppression of hydrogen evolution. Additionally, the formation of the second phase (Mg 17 Sr 2 ) facilitated the dissolution of the magnesium anode. However, when the Sr content was excessive, the second phase became coarse and continuous, leading to galvanic corrosion with the magnesium matrix and accelerated self-corrosion and uneven dissolution of the magnesium anode. Moreover, the inert film formed by SrO and SrCO 3 impedes the contact between electrolyte and Mg anode, thereby significantly reducing the discharge performance. Above analysis is confirmed by surface morphology after discharge, discharge products, electrochemical measurements, and hydrogen evolution tests. The Mg-0.1Sr alloy is identified as a highly promising anode material for magnesium-air batteries to balance the positive and negative effects of alloying element. This work demonstrates a simplified and cost-effective strategy for enhancing the performance of Mg-air batteries. • Mg 17 Sr 2 phase is a critical second phase to refine the Mg-air cell performance. • The Mg-0.1Sr alloy achieved a specific energy of 1872.1 Wh kg −1 . • Enhance the performance of Mg-air batteries by low-cost doping element.