A Study On The Preparation And Electrochemical Properties Of Mechanically Alloyed Ti-Cu Based Amorphous Hydrogen Storage Alloys

Based on the review of the research and development of the amorphous/nano-crystalline hydrogen storage materials as well as the amorphization synthesis of Ti-Cu based alloys, amorphous Ti-Cu based alloys by mechanical alloying in a planetary mill was explored.The purpose of this thesis is to synthesize amorphous Ti-Cu based alloys,Ti-Cu based alloys with Ni powder added and(Ti-Cu)+(Mg-Ni)composites,and investigate their phase structures and electrochemical properties by means of XRD,SEM,EDX and the electrochemical test methods including the galvanostatic charge-discharge,linear polarization and anodic polarization.The amorphous(Ti-Cu)+x wt%Ni(x=0,25,50,100)composites have been synthesized by mechanical ball-milling,using two different preparation methods:One is synthesized directly by mechanical alloying of Ti,Cu and Ni elemental powders;the other is synthesized by mechanical alloying of as-cast Ti₂Cu and Ni powders.The effects of Ni content and preparation methods on the phase structures and electrochemical properties of the milled samples have been investigated.The results show that Ni content and different preparation methods affect the phase structures and electrochemical properties of the samples markedly. Amorphous Ti₂Cu binary alloys cannot be synthesized directly from Ti and Cu elemental powders by mechanical alloying for 30-120h,and their discharge capacity are lower than 30 mAh/g.However,as Ni powder added,Ti₂Cu+ 100 wt%Ni composite become amorphization after milling for 80h,and the maximum discharge capacity reaches 100 mAh/g.On the other hand,the maximum discharge capacity of the crystalline Ti₂Cu as-cast alloy is only 3.7 mAh/g.It increases effectively as the as-cast Ti₂Cu is ball-milled with Ni powder for 120 h and forms an amorphous structure,such as the maximum discharge capacity is 82 mAh/g for the milled Ti₂Cu+50%Ni composite and 168 mAh/g for the milled Ti₂Cu+100%Ni composite.It is also found that ball-milling with the nickel powder and increasing grinding time are good for the amorphization of Ti₂Cu alloy.Furthermore,the nickel element in the composite plays a role of electro-catalysis and improves the electrochemical performance.Some novel composites have been synthesized by ball-milling Ti-Cu and Mg-Ni based compounds,and their phase structures and electrochemical properties have been investigated. The results show that the discharge capacity and cycling stability of the composite are greatly improve as amorphous MgNi is ball-milled with as-cast Ti₂Cu for 120h,the maximum discharge capacity of the Ti₂Cu+200 wt%MgNi milled composite reaches 326mAh/g,and the cycling retention rate after 20 cycles S₂₀is 53.3%;the maximum discharge capacity of the Ti₂Cu+100 wt%MgNi milled composite is 202mAh/g,and the cycling retention rate after 20 cycles S₂₀is 64.4%.As as-cast Ti₂Cu and TiCu are ball-milled with as-cast Mg₂Ni for 120 h respectively,both of them can not reach amorphization completely,the maximum discharge capacities of milled Ti₂Cu+100wt%Mg₂Ni and TiCu+100 wt%Mg₂Ni composites are 129 mAh/g and 47 mAh/g respectively.When Ni powder added,the amorphization degree of the milled composite and its discharge capacity are greatly improved,the maximum discharge capacity of milled Ti₂Cu+Mg₂Ni+50 wt%Ni and TiCu+Mg₂Ni+50 wt%Ni composites are 215 mAh/g and 269 mAh/g respectively.