A_2B_7型La_(0.75)Mg_(0.25)Ni_(3.5-x)Cr_x(x=0～0.3)贮氢合金相结构及电化学性能研究

A study on the structure and electrochemical properties of La_(0.75)Mg_(0.25)Ni_(3.5-x)Cr_x(x=0～0.3)

采用感应熔炼方法制备了La0.75Mg0.25Ni3.5-xCrx(x=0,0.05,0.1,0.2,0.3)四元贮氢合金,系统地研究了合金B端Cr元素对Ni部分替代对合金相结构及电化学性能的影响.X衍射(XRD)分析表明,La0.75Mg0.25Ni3.5合金是由La2Ni7相组成.随着Cr元素的加入,该类合金中出现LaNi5相及LaNi3相,且随着Cr含量的增加而增多.电化学测试表明,随Cr含量的增加,合金电极活化次数变化不大,最大放电容量逐步降低,合金的最大放电容量由x=0.05时的383.43 mAh/g下降到x=0.3时的348.40 mAh/g;而合金的高倍率放电性能呈现先增后减的趋势,当电流密度为900 mA/g时,合金的高倍率放电性能由83.66%(x=0)增加到92.57%(x=0.05)然后减小到83.9%(x=0.3);循环稳定性先增加后下降,当x=0.1时合金电极的循环寿命达到最大(S100=74.71%).

The effect of replacing part of the Ni by Cr element in La0.75Mg0.25Ni3.5 on the structure and electrochemical properties of thus formed La0.75Mg0.25Ni3.5-xCrx quaternary alloys （ x = 0,0.05,0.1,0.3） was investigated. XRD analysis shows that the La0.75Mg0.25Ni3.5 consists of La2Ni7 phase. LaNi3 phases and LaNi5 phases of CaCu5 type appeared when Cr was added. The Rietveld analysis shows that the increase of Cr content leads to an increase of the content of LaNi5 phase and LaNi3 phase. The electrochemical analysis shows that the substitutions lead to some decrease in the maximum discharge capacity ,with little effect on the activation property. For the discharge current density of 900 mA/ g, the high rate discharge ability （HRD） of the alloy electrodes increases from 83.66 % （x = 0） to 92.57 % （x = 0.05） and then decreases to 83.9% （x = 0.3） . The cyclic stability of alloy electrodes increase first and then decrease with increasing Cr content in alloys. S100 for La0.75Mg0.25Ni3.5-xCrx are 73.77%, 73.84% ,74.71% ,69.82% and 62.73%, respectively.