Effect On Structure And Electrochemical Properties Of Mg₂Ni Hydrogen Storage Alloy Doping With Different Amounts Of CeO₂ And Ni

Mg₂Ni hydrogen storage alloy has attracted much attention due to their excellent electrochemical hydrogen storage properties.Mg₂Ni hydrogen storage alloy has the advantages of large charging capacity and good charging performance.As the negative electrode of Ni-MH battery,it is an ideal material.The disadvantage is that the discharge condition is harsh,the discharge performance is poor,the discharge capacity is low,and the discharge cycle stability is also poor.Therefore,it is a problem need to be solved urgently that improve the electrochemical performance of Mg₂Ni hydrogen storage alloy.In view of the poor electrochemical performance of Mg₂Ni hydrogen storage alloy,some improvement methods are proposed in this dissertation.The optimization of preparation process and oxides and Ni doping are studied,and some valuable research results are obtained:?1?Doping with different rare earth oxides(CeO₂,La₂O₃,and Pr₆O₁₁)in Mg₂Ni hydrogen storage alloy and ball milling,it can be found that rare earth oxides not only increase the maximum discharge capacity of the alloy,but also improve the capacity retention rate.When doped with CeO₂,the alloy has the obvious improvement and the maximum discharge capacity,which is 163.58 mAh/g.We further improve the preparation process of the alloy?ball milling environment,rotation speed,and ball material ratio?,it is found that the ball milling in vacuum and the rotation speed and ball ratio are respectively 400 r/min and 20:1,the overall discharge performance of Mg₂Ni+1wt.%CeO₂ alloy is the best and the discharge capacity is 172.90 mAh/g.?2?Doping of different contents of Ce O₂ in the alloy,it is found that the catalytic effect is not obvious when the content of CeO₂ is less than 5wt.%.With the increase of doping content,the maximum discharge capacity of alloy increases firstly and then decreases.Doping with Ni and ball milled for 5 h can significantly improve the discharge performance of Mg₂Ni alloy on the basis of doping with 7wt.%CeO₂,but the amount of Ni exceeds 5wt.%,the discharge capacity of the alloy reduce.The maximum discharge capacity of the Mg₂Ni+7wt.%CeO₂+5wt.%Ni alloy is 224.60mAh/g,and the capacity retention rate is the maximum,which is 13.56%.After the electrode is fully charged and placed in an open circuit of 6 mol/L KOH solution for7×24 h,the charge retention rate?CRT?can still be as high as 68.93%.?3?The charge and discharge currents of the Mg₂Ni+7wt.%Ce O₂+5wt.%Ni alloy electrode are changed,it is found that discharge capacity of the alloy is the largest when the charge and discharge currents are 100 mA/g and 60 mA/g,respectively.?4?The performance of Mg₂Ni+7wt.%CeO₂+5wt.%Ni alloy with different ball milling time is investigated.The maximum discharge capacity of the alloy is 233.80mAh/g and the capacity retention rate is the lowest after milling for 10 h.The discharge capacities lower than 233.80 mAh/g of alloy when ball milled for 5 h and20 h,respectively.CRT of the alloy milled for 5h is the highest,which is 68.93%whereas CRT of the alloy milled for 20 h is lowest,only 62.75%.?5?SEM images and XPS atlas show that as the milling time increases,the alloy particles continuously decrease and agglomeration occurs,and the high-rate dischargeability?HRD?of the electrode gradually increases.But the HRD of the electrode decreases rapidly with the increase of the current,and the decrease trend of the HRD is most obvious when alloy by milling for 5h.