La_(2-x)MgNi_(9-5x)(x=0～1.0)贮氢合金的晶体结构与电化学性能研究

Crystal Structure and Electrochemical Properties of La_(2-x)MgNi_(9-5x) (x=0～1.0) Hydrogen Storage Alloys

系统研究了La2-xMgNi9-5x(x=0～1.0)合金的晶体结构与电化学性能。XRD及Rietveld全谱拟合方法分析表明,x=1.0时合金由单一相的LaMgNi4相组成,其余合金均由LaMgNi4与(La,Mg)Ni3相组成。随x的减小,合金中LaMgNi4相丰度递减,x=0.5时合金中主相变为PuNi3型(La,Mg)Ni3。在LaMgNi4相中,Mg占据4c位置,而在(La,Mg)Ni3相中Mg占据6c位置。电化学实验表明,合金氢化物电极放电容量随x的减小而增加,由x=1.0时的170mAh·g-1增加至x=0.0时的392mAh·g-1。

The crystal structure and electrochemical properties of La_(2-x)MgNi_(9-5x) (x=0～1.0) alloys were investigated by scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and electrochemical analysis. The experimental results reveal that all these alloys consisted of LaMgNi_4 phase and (La, Mg)Ni_3 phase except for the alloy with x=1.0, which consisted of a single LaMgNi_4 phase. The abundance of LaMgNi_4 phase decreased with the decrease of x value. XRD Rietveld refinement results indicat that element magnesium occupied preferentially the site 4c in LaMgNi_4 phase and the site 6c in (La, Mg)Ni_3 phase, leading to formation of partially ordered ternary compounds. Electrochemical experimental results show that the discharge capacity of the alloys decrease with increase of x value from 392 mAh·g^(-1) (x=0) to 170 mAh·g^(-1) (x=1). The coexistence of La, Mg)Ni_3 and LaMgNi_4 do not improve the electrochemical performance of LaMgNi_4 phase in the alloys.