The Study On The Corrosion Behavior And Discharge Performance Of Mg-Bi Based Anode Materials For Air Battery

Magnesium alloy is one of the most promising anode materials in metal-air batteries due to its series of advantages such as higher theoretical discharge voltage,specific capacity,energy density and light weight.However,the rapid self-corrosion rate of magnesium alloys,the low activity of products formed after discharge,and the short life of batteries have limited the application development of magnesium-air batteries to a certain extent.Studies have shown that Mg-Bi-based alloys have good corrosion resistance,but no one has done relevant research on the negative electrode of air batteries.In this paper,the structural characteristics and discharge performance of Mg-Bi-based alloys are studied by means of alloying and deformation processes,which provides a potential new anode material for the study of anode materials for magnesium-air batteries.Through the composition optimization design of Mg-Bi alloy system,combined with the extrusion deformation to adjust the structure and properties of the alloy.Through tissue characterization and analysis,corrosion behavior and discharge behavior research,the best alloy system suitable for the anode material of magnesium air battery was determined based on the criteria of anode efficiency,discharge activity and stability.(1)First,four Mg-xBi(x=0.5,1.0,1.5,2.0)binary alloys are designed.The results show that with the increase of Bi element content,the finely dispersed second phase(Mg₃Bi₂)phase in the alloy Increase,the alloy's grain size decreases.On the one hand,the Bi element has the effect of refining the crystal grains,on the other hand,the finely dispersed second phase can play a role of pinning the grain boundaries and hinder the growth of the crystal grains.In addition,with the increase of the Bi element content,under the condition of small current density,the discharge voltage of the Mg-Bi binary alloy as the negative electrode material of the air battery changed from-1.61V to-1.65V,and the anode efficiency increased from 40.21%to 49.32%,Under the condition of large current density,the discharge voltage changes from-1.42V to-1.58V,and the anode efficiency increases from 63.82%to 71.4%.Therefore,the Mg-2.0Bi alloy exhibits the best discharge performance.(2)Based on the Mg-2.0Bi binary alloy as the base alloy,three extruded states Mg-2.0Bi-0.5Ca,Mg-2.0Bi-0.5In and Mg-2.0Bi-0.5Ca-0.5In alloy were prepared by alloying Ca and In elements.The results show that the addition of Ca makes the discharge products of the alloy thin and cracked.The addition of In promotes the combination of the electrolyte and the discharge products and improves the electrochemical activity of the alloy.In addition,the discharge product of Mg-2.0Bi-0.5Ca-0.5In alloy is mainly composed of Mg(OH)₂and Ca O.The alloy added with Ca and In composites shows a dispersed texture type.This dispersed texture weakens the texture to a certain extent,thereby improving the discharge performance of the alloy.Therefore,the alloy added with Ca and In shows the best discharge performance.(3)In order to further optimize the alloy design and reduce the adverse effects of the second relative alloy discharge activity,a low alloyed Mg-1.0Bi-x Ca(x=0,0.5)alloy was designed and its microstructure characteristics and discharge behavior were studied.The results show that,compared with the Mg-1Bi alloy,the Mg-1Bi-0.5Ca alloy shows a more negative discharge potential and a higher anode efficiency.In addition,the discharge morphology of Mg-1Bi-0.5Ca alloy is loose and thin,and many cracks appear on the surface of the alloy.These features promote the penetration of Na Cl solution and enhance the discharge activity of the alloy.In addition,when Mg-1Bi-0.5Ca alloy is used as the negative electrode of magnesium-air batteries,it shows higher battery voltage and power density at all current densities.Therefore,the extruded Mg-1Bi-0.5Ca alloy is an ideal anode material for magnesium-air batteries.