化学计量比La/Mg对铸态及退火态La-Mg-Ni系A2B7型电极合金结构及电化学性能的影响

摘要

In order to investigate the influences of the stoichiometric ratio of La/Mg (increasing La and decreasing Mg on the same mole ratio) on the structure and electrochemical performances of the La−Mg−Ni-based A2B7-type electrode alloy, the as-cast and the annealed ternary La0.8+xMg0.2–xNi3.5 (x=0−0.05) electrode alloys were prepared. The characterization of electrode alloys by X-ray diffraction (XRD) and scanning electron microscopy (SEM) shows that all the as-cast and the annealed alloys hold two major phases of (La,Mg)2Ni7 and LaNi5 as well as a residual phase of LaNi3. Moreover, the increase of La/Mg ratio brings on a decline of (La,Mg)2Ni7 phase and a rise of LaNi5 and LaNi3 phases. The variation of La/Mg ratio gives rise to an evident change of the electrochemical performances of the alloys. The discharge capacities of the as-cast and the annealed alloys evidently decrease with growing the La/Mg ratio, while the cycle stabilities of the alloys visibly augment under the same condition. Furthermore, the high rate discharge ability (HRD), the electrochemical impedance spectrum (EIS), the Tafel polarization curves, and the potential step measurements all indicate that the electrochemical kinetic properties of the alloy electrodes increase with the La/Mg ratio rising.%采用合金熔炼及退火处理的方法制备La−Mg−Ni系 A2B7型La0.8+xMg0.2–xNi3.5(x=0−0.05)电极合金，并研究不同的化学计量比 La/Mg 对该合金的相结构和电化学性能的影响。通过 X 射线衍射(XRD)和扫描电子显微镜(SEM)对合金进行表征。结果表明：合金包含(La, Mg)2Ni7和LaNi5两个主相以及一些残余相LaNi3。随着La/Mg比率的增大，合金中的(La, Mg)2Ni7相含量降低，而LaNi5和LaNi3相的含量升高。La/Mg比的变化也使得合金电极的电化学性能发生显著变化。随着La/Mg比率的增加，铸态及退火态合金的放电容量降低，而循环稳定性明显改善。此外，合金电极的高倍率放电性能(HRD)、电化学阻抗谱(EIS)、Tafel极化曲线以及电势阶跃的测量均表明La/Mg比率的增加提高了合金的电化学动力学性能。