The Study On Anode Performance Of Mg-air Batteries Based On Mg-In And Mg-Al Alloys

In today’s increasingly depleted resources,the search for excellent alternative energy sources has become an important issue to be solved urgently.Magnesium（Mg）air battery with Mg and its Mg alloy as anode is an emerging metal air battery,which has the advantages of high theoretical voltage,high theoretical specific capacity and high theoretical specific energy.There are still two major challenges in the research to enhance the discharge performance of Mg-air battery anodes.First,due to the active chemical property of Mg,the Mg anode will self-corrode in the electrolyte solution during the discharge process of the anode.The Mg consumed by self-corrosion is not available for discharge,therefore,self-corrosion can seriously reduce the anode utilization of the cell.As self-corrosion accelerates the consumption of Mg anode,so the service life of the battery will also be greatly reduced.Secondly,the anode will produce a large amount of discharge products mainly Mg（OH）₂ during the discharge process,and as the discharge continues,the discharge products will also continue to accumulate in the anode,which will eventually cause serious anodic polarization.At present,the main solutions to solve the above two problems are alloying and upgrading the performance of Mg itself two solutions.Indium（In）has stable chemical properties,which are important in enhancing the discharge activity and corrosion resistance of Mg.According to the current research,the addition of aluminum（Al）element in Mg can not only enhance the mechanical strength of Mg,but also enhance the corrosion resistance of Mg.Meanwhile,the Mg-Al alloy has become a very mature alloy system through the research of researchers.Through the research,it is found that the heat treatment and plasticity densification process can regulate the microstructure of Mg and enhance the corrosion resistance of Mg.Therefore,this thesis will add other alloying elements based on Mg-In and Mg-Al alloys,and regulate the microstructure of the experimental alloy through heat treatment and hot extrusion to further improve the discharge performance and corrosion resistance of the anode.The specific studies are as follows.（1）First,a series of Mg-In alloys with different compositions were prepared by conventional melting and other means to study the effects of In content on the microstructure as well as the discharge properties of the alloys.Then the microstructure of the alloys was further improved by solid solution treatment of Mg-In alloys.The specific conclusions are as follows:there is no second phase in the Mg-In alloy,and the as-cast alloy is mainly dominated by dendrites,which change to equiaxed grains after the solid solution treatment.The cell discharge experiments revealed that the discharge voltage and anode utilization rate of Mg-3In alloy are higher than those of pure Mg,which is due to the more sparse discharge product layer and uniformly dissolved surface of Mg-3In alloy.（2）The effect of Calcium（Ca）content on the microstructure and discharge properties of Mg-In alloys was investigated,and the effect of hot extrusion on the microstructure and discharge properties of Mg-In-Ca alloys was studied.The specific conclusions are as follows:the addition of Ca obviously refines the alloy grain,and also introduces the second phase Mg₂Ca phase,which is mainly distributed at the grain boundaries,and after the hot extrusion treatment,the Mg₂Ca phase is squeezed and diffusely distributed in the Mg matrix.Among them,the Mg-3In-3Ca alloy has excellent anode utilization and specific capacity,which is attributed to the refinement of the grain size of the alloy by the addition of Ca.The compositional analysis of the surface of the removed discharge products revealed that a large amount of In was deposited on the surface,which significantly reduced the adsorption force between the discharge products and the anode and formed a more sparse discharge product layer.Meanwhile,the appearance of Mg₂Ca phase accelerated the dissolution of the Mg matrix,and the uniformly distributed Mg₂Ca phase made the anode dissolution more uniform.（3）The effect of Tin（Sn）content on the microstructure and discharge properties of Mg-Al alloy was studied,and the effect of hot extrusion on the microstructure and discharge properties of Mg-Al-Sn alloy was investigated.The specific conclusions are as follows:After adding Sn to the anode of Mg-Al alloy,the anode utilization and specific capacity were improved.However,when the Sn content is too high,the anode utilization rate of the Mg-Al-Sn alloy decreases because the Mg₂Sn phase content is too high,and the Mg₂Sn phase can increase the hydrogen precipitation rate and reduce the corrosion resistance of the Mg-Al-Sn alloy.After hot extrusion of the Mg-Al-Sn alloy,the anode utilization rate of the alloy was slightly reduced.The reticulated Mg₁₇Al₁₂ phase,which is a barrier against corrosion,was extruded during the extrusion process,and the ability to resist corrosion was weakened,resulting in a weaker anodic utilization of the alloy.However,the discharge products formed on the surface of the extruded alloy are more sparse,and the surface dissolution of the removed discharge products is more uniform,which is easy to shed the discharge products.On the contrary,the corrosion surface of the cast Mg-Al-Sn alloy has a mesh structure,and there are a large number of corrosion gaps,which can store the discharge products,which is not conducive to the shedding of the discharge products.By reviewing the relevant literature,the latest research progress of Mg-air battery is briefly summarized,and the low anode utilization rate of Mg-air battery still exists.However,the Mg-3In-3Ca alloy prepared in this thesis has a high anode utilization rate,and the Mg-3In-3Ca alloy has the highest anode utilization rate among the summarized anode alloys,which provides a reference for the subsequent research on Mg-air batteries.