Study On Structur And Electrochenmica Properties Of La-Ni-Al Hydrogen Storage Alloys

The overall properties of La-Ni-Al alloys have been investigated on the basis ofcomprehensive review of the research progress of hydrogen alloys. In this work, series ofLaNi4.1Al0.17+x wt.%M (x=0，1.0，2.0，4.0，M=B，Nd，Gd，Ce) hydrogen storage alloysare prepared by arc induction melting. The microstructure of the alloys have been studiedby XRD、 SEM-EDS. Galvanostatic method and EIS have been used to measureelectrochemical properties. The following contents have been systematically studied:(1)The effect of B addition on the structure and electrochemical performances of thealloy;(2)The effect of ball-milling on the structure and electrochemical properties of thealloy;(3)The effect of rare earth elements addition on the microstructure andelectrochemical properties of the alloy.The results show that the LaNi4.1Al0.17alloy is composed of LaNi5phase with CaCu5structure、La2Ni7phase with Ce2Ni7structure and LaNi3phase withPuNi3structure. Thecrystal structure of the main phase has been changed after B addition, and theLaNi4.1Al0.17+x wt.%B (x=1.5，2.0，2.5) alloys are composed of LaNi5phase and La2Ni7phase.The addition of B improves the cycle stability of alloy electrodes with the capacityretention increasing from55.67%(x=0) to79.1%(x=2.0). The B addition can enhancethe high rate discharge capacity of the alloy elecreodes while decrease the the chargetransfer resistance. The HRD is up to maximum when the B content is2.0%.In this study,ball-milling is used in order to improve the electrochemical propertiesof LaNi4.1Al0.17B0.03alloy. The effect of the milling time on electrochemicalperformances of the alloy has been investigated. Electrochemical sudies show that theactivition characteristic of the ball-milled alloys is noticeably improved. The alloyelectrode has better maximum discharge capacity when ball-milling time is less than120min. The maximum discharge capacity of the electrode reaches335.8mAh/g whenmilling time is30min. Although the cyclic stability of the ball-milled alloys decrease,the capacity retention rate of the alloy electrodes increase with the increasing ball-millingtime, for example, the capacity retention rate of30th cycle increases from71.41%(30 min) to82.14%(300min). Ball-milling can enhance the high rate dischargeability of thealloy electrode.The effect of rare earth elements Nd、Gd and Ce addition on the electrochemicalcharacteristic of alloy electrodes are different. The alloys consist of LaNi5phase、La2Ni7phase and LaNi3phase with Nd and Gd addition,and the content of La2Ni7phase increasewith Nd and Gd addition. The alloys with Ce addition are composed of LaNi5phase andLa2Ni7phase. Rare earth elements can improve the cycling life of the electrodes. Thecapacity retention rate increases with increasing Nd content.The alloys with Gd and Ceadditon reach their maximum capacity retention rate when the content is2.0%. Theaddition of Nd and Ce can improve the self-discharge property. The define amount of rareearth elements can enhance the high rate dischargeability. The HRD of all the alloyelectrodes increase firstly and then decease with the increasing contents of additiveelements. The HRD of the alloys with Nd、Gd and Ce addition reach the maximum andthe charge transfer resistance achieves the minimum at1.0%、2.0%and2.0%,respectively.