Investigation On The Phase Structure And Electrochemical Performances Of Ball-milled La₂Mg₁₇ Composite Hydrogen Storage Material

Recently, Mg-based hydrogen storage alloys have been regarded as the third new generation of promising hydrogen storage alloys because of their high hydrogen storage capacity, abundant resources and light weight, and have become the study hotspot at home and abroad. Based on the review of the research and development of the Mg-based hydrogen storage alloys, La₂Mg₁₇ hydrogen storage alloy was selected as the study object of this work due to its higher storage capacity than Mg-Ni system alloy. However, the application of La₂Mg₁₇ alloy in the electrochemical hydrogen storage can hardly be performed because of its poor kinetic properties and high hydride stability.In this thesis, the microstructure and electrochemical properties of the amorphous La₂Mg₁₇+200wt.%M(M=Ni or Cu)+1wt.%CeO composites prepared by ball-milling time. By means of XRD, SEM and DSC analyses and the electrochemical test methods including the galvanostatic charge-discharge, EIS and polarization etc.. The study includes the followings:The study of the influence of Ni/Cu amounts and ball-milling time on the microstructure and electrochemical properties of La₂Mg₁₇ composite alloys revealed that ball-milling with certain amount of Ni/Cu can make La₂Mg₁₇ alloy a good activation performance and high storage capacity by ball-milling in the Ar. The electrochemical measurements indicate that after 30h ball-milling the La₂Mg₁₇+200wt.%Cu+1wt.%CeO composite exhibited a max discharge capacity of 134mAh.g^-1, but the La₂Mg₁₇+200wt.%Ni+1wt.%CeO composite exhibited a max discharge capacity of 934.3mAh.g^-1 with the increase of ball-milling time from 10 to 40h. And the discharge potential characteristics of the two composites are markedly improved with prolonging of ball-milling time. HRD at Id = 400 mA.g^-1 of the composite plating Cu is 68% of that at 100mA.g^-1 when ball-milling is 30h, which is 15.9% higher than the 10h, and HRD at Id = 400mA.g^-1 of the composite plating Ni is 81% of that at 100mA.g^-1 when ball-milling is 30h, which is 16.1% higher than the 10h. It is found that ball-milling with adequate amount Ni/Cu powders is advantageous for the formation of amorphous structure, thus leading to the improvement of thermodynamic and kinetic properties of the ball-milled composites. The discharge capacity of the amorphous composite is influenced by both the amorphization degree and particle size. There exist an optimal Ni and Cu amount and ball-milling time for the achievement of the highest discharge capacity. Before the optimal value, the discharge capacity is mainly influenced by the amorphization degree, and beyond the optimal one, the particle size becomes the dominating factor.