Al替代Mg对La2MgNi7.5Al1.5贮氢合金相结构和电化学性能的影响

采用X射线衍射、电子探针和电化学测试研究了La2Mg1-xAlxNi7.5Co1.5(x=0.0,0.1,0.3,0.5)合金的相结构和电化学性能.XRD结果和EPMA观察表明,少量的Al替代Mg(x=0.1)不改变La2MgNi7.5Co1.5合金的相组成,合金仍然由LaNi3相和αLa2Ni7相组成,然而La2Mg0.9Al0.1Ni7.5Co1.5合金中LaNi3相的丰度明显下降,αLa2Ni7相的丰度则增加,较多的Al替代Mg改变了La2MgNi7.5Co1.5合金的相组成并导致合金中LaNi3相消失,La2Mg1-xAlxNi7.5Co1.5合金中Al含量的变化对合金中不同相晶胞参数的影响不相同.此外,少量的Al替代Mg(x=0.1)几乎不降低La2MgNi7.5Co1.5合金的贮氢容量和最大电化学放电容量,但随La2Mg1-xAlxNi7.5Co1.5合金中Al含量的增加,合金的贮氢容量、最大电化学放电容量和活化性能不断下降,Al替代Mg能明显提高La2MgNi7.5Co1.5合金的电化学循环稳定性,对提高该合金电极的高倍率放电性能也是有利的.

Influence of Al Substitution for Mg on Phase Structure and Electrochemical Properties of La2MgNi7.5Co1.5 Hydrogen Storage Alloys

The phase structure and electrochemical properties of La2Mg1-xAlxNi7.5Co1.5 (x=0.0,0.1,0.3,0.5) alloys were investigated by means of X-ray diffraction (XRD), electron probe X-Ray microanalysis (EPMA) and electrochemical measurements. XRD and EPMA results show that small quantity replacement Mg by Al (x=0.1) does not change phase composition of La2MgNi7.5Co1.5 alloy, the alloy is still constituted with LaNi3 phase and αLa2Ni7 phase, but the abundance of LaNi3 phase decreases obviously and that of αLa2Ni7 increases in the La2Mg0.9Al0.1Ni7.5Co1.5 alloy. The more Al substitution will change phase composition of the alloy, resulting in LaNi3 phase disappearance. Influence of change of Al content on cell parameters of different phases of the La2Mg1-xAlxNi7.5Co1.5 alloy is different. Moreover, little replacement of Mg by Al (x=0.1)lowers scarcely hydrogen storage capacity and maximum electrochemical discharge capacity of the alloy, but with the increment of Al content in the La2Mg1-xMgxNi7.5Co1.5 alloy, hydrogen storage capacity, activation property and maximum electrochemical discharge capacity of the alloys decrease continuously. Al substitution for Mg can improve obviously electrochemical cyclic stability of La2MgNi7.5Co1.5 alloy electrode, and is beneficial to improve high rate dischargeability of the alloy electrode.