La0．67Mg0．33Ni3．0-xAlx（x=0～0．3）贮氢合金的相结构及电化学性能的研究

A study on the structure and electrochemical properties of La_(0.67)Mg_(0.33)Ni_(3.0-x)Al_x(x=0,0.1,0.2,0.3) hydrogen storage alloys

研究了Al元素对合金La0.67Mg0.33Ni3.0中Ni的替代对合金的微观组织结构及电化学性能的影响.X射线衍射(XRD)分析结果表明,La0.67Mg0.33Ni3.0合金由PuNi3型(La,Mg)Ni3相和Ce2Ni7型(La,Mg)2Ni7相组成 ,Al元素加入后,开始出现CaCu5型LaNi5相,随着Al含量的增加,LaNi5相逐渐增多,当x=0.3时,LaNi5相成为合金的主相,合金La0.67Mg0.33Ni2.7Al0.3中Al的X荧光元素面分布图像表明了Al元素主要进入LaNi5相中,说明Al是一种LaNi5相形成元素;电化学测试表明,随着Al含量的增加,合金的最大放电容量依次下降,4种合金的最大放电量分别为392、324、267和252mAh/g,活化次数变化不大(2～3次即可活化),循环稳定性先增加后下降.

The effect of replacing part of Ni by Al in La_(0.67)Mg_(0.33)Ni_(3.0) on the structure and electrochemical properties of thus formed La_(0.67)Mg_(0.33)Ni_(3.0-x)Al_x quaternary alloys(x=0,0.1,0.2,0.3) was investigated.XRD analysis shows that La_(0.67)Mg_(0.33)Ni_(3.0) consists of(La,Mg)Ni_3 phase and(La,Mg)_2Ni_7 phase.LaNi_5 phase with CaCu_5 type appeared when Al was added.The increase of Al content leads to an increase of content of LaNi_5 phase.The main phase of the Al substituted alloys with x=0.3 was LaNi_5 phase.The Rietveld analysis for La_(0.67)Mg_(0.33)Ni_(3.0-x)Al_(0.1) shows that Al atoms occupy 6h position which was between two CaCu_5 units in(La,Mg)_2Ni_7 phase.The results of EPMA analysis for La_(0.67)Mg_(0.33)Ni_(3.0-x)Al_(0.3) reveal that Al mainly substitutes the Ni in LaNi_5 phase.We can draw a conclusion that Al was helpful to the formation of LaNi_5 phase.The electrochemical analysis shows that the substitutions lead to some decrease in discharge capacity and have little effect on the activation property.The discharge capacity of La_(0.67)Mg_(0.33)Ni_(3.0-x)Al_x(x=0,0.1,0.2,0.3) are 392,324,267 and 252mAh/g respectively.S50 for La_(0.67)Mg_(0.33)Ni_(3.0-x)Al_x(x=0,0.1,0.2,0.3) were 78.4%,82.4%,(83.5%) and 77.5% respectively.