Effect Of In And Bi Compound Addition On Electrochemical Performance And Discharge Behavior Of Extruded Mg-Al Based Anode Materials

The magnesium-air battery has the advantages of no pollution,non-toxic,theoretical voltage and high specific energy,etc.,and is regarded as an ideal new energy source.Mg-Al-based anode materials with low cost and corrosion resistance have received extensive attention.In this paper,the addition of In and Bi elements to Mg-Al-based alloys combined with forward extrusion and equal channel angular extrusion(ECAP)deformation improves the microstructure of the alloy,and the alloy elements In and Bi on the Mg-Al-based alloy microstructure and The influence of the electrochemical performance,through analyzing the electrochemical behavior of the alloy,reveals the influence of the alloy element,grain size and second phase synergy on the discharge activity and utilization rate of the extruded Mg-Al-based anode.By observing the surface morphology of the magnesium anode material after discharge,the dissolution mechanism of the magnesium anode material during discharge was explored.Finally,the discharge performance of the magnesium-air battery with Mg-Al-based alloy as the anode was tested to reveal the internal relationship between the evolution of the structure and the change in discharge performance.The specific research results are as follows:0.5?1.0 wt.%In element is added to the positively extruded Mg-9Al alloy and is evenly distributed in the magnesium matrix.No new phase containing In element is formed,which effectively promotes alloy grain refinement and the number of Mg₁₇Al₁₂ precipitated phases Increase,the size decreases;and with the increase of In content,the grain size of the positively extruded Mg-9Al alloy first decreases and then increases,the area fraction of the precipitated phase of Mg₁₇Al₁₂ in the alloy first increases and then decreases,the average size of the precipitated phase of Mg₁₇Al₁₂ It decreases first and then increases;the synergistic effect of the dissolution and re-deposition of In element,a large number of fine-sized Mg₁₇Al₁₂ precipitates and fine grain size leads to an increase and then a decrease in the utilization rate of the alloy in the constant current discharge test.The Mg-9Al-0.5In anode material with the best discharge performance has a power density and specific capacity of 32.25m W/cm² and 1164 mAh/g,respectively.In order to further improve the Mg-Al-based anode discharge performance,Bi element(0.5?2.0 wt.%)Is added to the Mg-9Al-0.5In alloy.After the addition of Bi element,high-melting granular and long rod-shaped Mg₃Bi₂phases are formed in the alloy And the long rod-shaped Mg₃Bi₂ phase is distributed in a strip shape parallel to the extrusion direction,and the grain size of the extruded Mg-9Al-x Bi-0.5In alloy gradually decreases with the increase of Bi content.The grain size leads to a higher grain boundary area,corroded micro-couples formed by the Mg₃Bi₂ phase and the Mg₁₇Al₁₂ phase with the magnesium matrix,respectively,and the uniform dissolution of the magnesium anode during discharge makes the Mg-9Al-x Bi-0.5In alloy in the constant current discharge test The utilization rate in the system increases first and then decreases.The power density and specific capacity of the extruded Mg-9Al-1.5Bi-0.5In anode material were 38.6 m W/cm² and 1386.81 mAh/g,respectively.Equal channel angular extrusion(ECAP)is beneficial to the grain size refinement of the positively extruded Mg-9Al-1.5Bi-0.5In alloy and promotes the precipitation of the Mg₁₇Al₁₂phase,and can improve the distribution of the strip-shaped Mg₃Bi₂ phase in the alloy.As the number of ECAP deformation passes increases,the grain size of the alloy gradually decreases.When the alloy is discharged at a high current density(120mA/cm²),the potential shifts significantly positively and undergoes periodic violent fluctuations,and the utilization rate of the alloy after ECAP deformation decreases significantly.The ECAP deformed 2-pass Mg-9Al-1.5Bi-0.5In anode material with the best discharge performance has a power density and specific capacity of 43.2m W/cm² and 1478 mAh/g,respectively.