Al元素对储氢合金RE0.8Mg0.2(Ni0.85-xCo0.15Alx)3.5的结构及电化学性能的影响

Effect of Al Content on Structure and Electrochemical Characteristics of Re0.8Mg0.2(Ni0.85-xCo0.15Alx)3.5 Hydrogen Storage Alloys

摘要:

用感应熔炼法制备了La0.5Pr0.2Nd0.1Mg0.2(Ni0.85-xCo0.15Alx)3.5(x=0.01~0.04)合金，并在氩气气氛下，用900 ℃退火处理。XRD分析表明，合金有两个主相：La2Ni7相和LaNi5相，晶轴比c/a随着Al含量的增大而增大。电化学测试表明，放电容量随着Al含量的增大而减小，由x=0.01时的394.6 mAh/g下降到x=0.04时的380.6 mAh/g，充放电循环衰减速率由x=0.01时的–0.32 mAh/(g·cycle)降为x=0.04时的–0.2

Abstract:

Hydrogen storage alloy La0.6Pr0.2Mg0.2(Ni0.85-xCo0.15Alx)3.5(x=0, 0.01, 0.02, 0.03, and 0.04) were prepared by induced melting method followed by annealing treatment at 900 ℃. The effects of partial substitution Al for Ni on the structure, electrochemical properties of the alloys were investigated systematically. X-ray diffraction (XRD) results indicate that the alloys were composed of La2Ni7 and LaNi5 phase with the Ce2Ni7-type and CaCu5-type structure. The value of c/a increases with the increase of Al content. The electrochemical analysis shows that the increase of Al leads to some decrease in both the discharge capacity and the HRD (high-rate dischargeability), but leads to a significant improvement in cycling stability of alloys. The discharge capacity decreases from 394.6 mAh/g (x=0.01) to 380.6 mAh/g (x=0.04), and the HRD decreases from 61% (x=0.01) to 35% (x=0.04) as the electrodes were discharged at 1200 mA/g. However, the rate of attenuation decreases from –0.32 mAh/(g·cycle) (x=0.01) to –0.20 mAh/(g·cycle) (x=0.04). This research reveals higher discharge capacity was remained, and cycling stability was improved remarkably when x≤0.02