A2B7型La0.75Mg0.25Ni3．5-xAlx（x=0-0．3）合金相结构及电化学性能

摘要:

采用感应熔炼方法制备了A2B7型La0.75Mg0.25Ni3．5-xAlx（x=0，0．02，0．06 0.1，0．3）四元贮氢合金，系统研究了Al元素部分替代Ni对A2B7型La0.75Mg0.25Ni3．5合金相结构及电化学性能的影响。X射线衍射（XRD）分析表明：La0.75Mg0.25Ni3．5由单一La2Ni7相组成：Al元素加入后，开始出现CaCu5型LaNi5相，当x=0．3时，LaNis相成为合金的主相。Rietveld分析表明：随着Al含量的增加，LaNi5相逐渐增多，Al的加入利于CaCu5型LaNi5相的形成。电化学测试表明：Al替代Ni对A2B7型合金La0.75Mg0.25Ni3．5电极活化性能影响不大：而最大放电容量随Al在La0.75Mg0.25Ni3．5-xAlx，合金中替代量的增加而减小。当放电电流密度为1600mA／g时，合金的倍率放电性能由68.8％（x=0）增加到81．16％（x=0．1）然后减小到65．67％（x=0.3）。此外，La0.75Mg0.25Ni3．5-xAlx合金电极循环稳定性先增加而后下降。x=0．06时合金电极容量保持率最大（S100=85.21．％）。

Abstract:

Quaternary Hydrogen Storage Alloys La0.75Mg0.25Ni3.5-xAlx(x=0,0.02,0.06,0.1,and 0.3) of A2B7 type were prepared by induced melting method.The effects of partly replacing Ni by Al element in La0.75Mg0.25Ni3.5 on the phase structure and electrochemical properties of La0.75Mg0..25Ni3.5-xAlx quaternary alloys were investigated.XRD analysis shows that the La0..75Mg0.25Ni3.5 consists of single(La,Mg)2Ni7 phase,the LaNi5 phases of CaCu5 type appears when Al was added to substitute Ni,and becomes the main phase when x=0.3.The Rietveld analysis shows that the increase of Al content leads to an increase of LaNi5 phase.We can draw a conclusion that the Al element is helpful to the formation of LaNi5 phase.The electrochemical analysis shows that the substitutions of Al lead to some decrease of maximum discharge capacity and a little effect on the activation property.For a discharge current density of 1600 mA/g,the high rate discharge(HRD) ability of the alloy electrodes increases from 68.80%(x=0) to 81.16%(x=0.1),then decreases to 65.67%(x=0.3).The cyclic stability of alloy electrodes increases firstly,then decreases with increasing the Al content in alloys.The parameter S100 for La75Mg0.25Ni3.5-xAlx(x=0,0.02,0.06,0.1,and 0.3) are 73.77%,77.69%,85.21%,7 0.26% and 70.96%,respectively.