Study On Discharge Performance Of Mg-Sn Alloys Anodes And Electrolyte Modification For Mg-air Batteries

With the increasingly serious problems of energy shortage and environmental pollution,the goal of carbon neutrality and carbon peaking is becoming more and more realistic.Non-carbon fuel cells are one of the best solutions to these two problems.An Mg-air battery is a high-efficiency fuel cell system using metal Mg as fuel.Due to the advantages of environmental friendliness,reusability,easy assembly,abundant raw materials,high theoretical battery voltage and energy density have attracted significant attention from domestic and foreign industries.However,the low anode efficiency corresponding to the self-corrosion of Mg and the high polarization induced by the deposition of dense discharge product films on the surface of Mg anodes significantly reduce the inherently excellent discharge performance of Mg-air batteries.Generally,the microstructure,processing process,and electrolyte properties of Mg alloy anodes greatly influence the discharge performance of batteries.Previous studies have shown that the high hydrogen evolution overpotential of the green element Sn can effectively inhibit the self-corrosion of the Mg matrix.At the same time,it combines with Mg to form a stable Mg₂Sn phase,which can be used as an activation point to promote the dissolution of the Mg anode and the cracking and peeling of the discharge product film.This paper investigates the electrochemical behavior and discharge performance of Mg-Sn alloys through microstructure observation,electrochemical performance analysis,and assembled battery testing.And the comprehensive discharge performance of Mg-air batteries was further improved by optimizing the preparation process and electrolyte solution additives.The specific research work of this paper is as follows:（1）The effect of Sn content on the microstructure evolution and discharge performance of as-cast Mg-xSn（x=1,5,9 wt.%）alloys were investigated.The results show that with the increase of Sn content,the volume fraction of the Mg₂Sn phase increases,promoting dendrite refinement and intensifying the segregation degree of Sn element.For the Mg-1Sn alloy,the micron-scale Mg₂Sn phase dispersed in the Mg matrix and the relatively negative open circuit potential is beneficial to the Mg anode’s uniform dissolution and discharge activity,which improves the anode efficiency and discharge potential.As a result,the Mg-1Sn anode exhibited a better average discharge voltage,anode efficiency,specific capacity,and energy at each tested current density in the discharge performance test.（2）The effect of extrusion temperature on the microstructure and discharge properties of Mg-Sn alloys was studied.The discharge properties of Mg-5Sn and Mg-1Sn alloys extruded at 350℃were compared to reveal the relationship between alloy microstructure and discharge properties.The results show that dynamic recrystallization promotes alloy grain refinement and secondary phase refinement during extrusion.Among the Mg-5Sn alloys,the anode efficiency and discharge voltage are better when extruded at 350°C.The fine and dispersed second phase in the extruded Mg-1Sn anode promotes the uniform dissolution of the Mg matrix and weakens the"block effect";the strong electrochemical activity is beneficial to the improvement of the discharge voltage.Therefore,the anode efficiency,specific capacity and energy density are improved compared with the Mg-5Sn anode.（3）The effect of adding a mixture of salicylic acid（SAL）and sodium nitrate（NaNO₃）（MIX）at different concentrations in 3.5 wt.%Na Cl solution on the discharge performance of the extruded Mg-1Sn anode alloy was investigated.The results show that the anode efficiency of the battery is improved at each tested current density,and the anode efficiency increase is more pronounced as the MIX concentration increases.Especially at 0.5 m A cm^-2,the utilization efficiency of mg anode increased from 30.7%of blank Na Cl solution to82.6%at a MIX concentration of 0.1 M.At the same time,the discharge voltage was raised from 1.553 V to 1.658 V.When the current density is greater than 0.5 m A cm^-2,the battery discharge law is just the opposite.