Structure And Electrochemical Performance Of Mg-Based Hydrogen Storage Alloy Used As Negative Electrode Material In MH/Ni Battery

Mg-based hydrogen storage alloy (eg. Mg₂Ni) has virtues of high capacity and low price. The theoretical capacity of Mg₂Ni is 3.6wt%, which is higher than the capacity of other hydrogen storage alloy. It is considered as a promising hydrogen storage material owing to its light weight and abundance in natural resources. However, the alloy of crystal Mg₂Ni cannot desorb hydrogen under ambient condition and shows poor kinetics performance. Mg₂Ni alloy has instable chemical characteristics, which results in erosion in high concentration alkaline solution at higher temperature. So Mg₂Ni alloy has poor stability. The purpose of this work is to improve electrochemical performance of Mg₂Ni alloy. Mg-based hydrogen storage alloy were systemically studied in the light of deeply understanding of current status of hydrogen storage alloy performed at home and abroad. Mg₂Ni alloy with different ball-milling time is prepared by means of MA. Moreover different type alloys, such as AB₅, AB₃ and solid solution were added to Mg₂Ni alloy to synthesize the composite alloy. A little Mg₂Ni was added to Ti_0.8Zr_0.1Mn_0.5V_1.0Cr_0.2Ni_0.3 solid solution in order to improve the activation of it. Different ball-milling time effect on electrochemical performance of Mg₂Ni alloy, as well as improved performance of composite alloy and influence of addition of Mg₂Ni on the solid solution alloy, is investigated by measuring electrochemical capacity,HRD and charge retention. The alloy powder was characterized by X-ray diffraction (XRD), and the scanning electron microscope (SEM) was used for examining the alloy powder's morphology. It is shown that Mg₂Ni alloy is multicrystal, and amorphous alloy appears with increasing ball-milling time, and the dischargeability of the alloy is dramatically increased owing to amorphous structure. Mg₂Ni composite alloy has new performance not available to a single alloy. During the alloying process the ball-milling makes each phase of the composition produce new hydrogen storage performance. It is revealed that the stability of the composite alloy is increased, and electrochemical characteristics of the composite with AB₅ type is best; the activation time of Ti_0.8Zr_0.1Mn_0.5V_1.0Cr_0.2Ni_0.3 composite alloy is reduced but the cycle stability decreases.