Study on Electrochemical Properties of Annealed R0.67Mg0.33Ni3.0 (R= La, Ce, Pr, Nd) Hydrogen Storage Alloys

Through substitution of mixed rare earth elements Ce, Pr and Nd for La, (La0.7Ce0.1PrxNd2-x)(0.67)Mg0.33Ni3.0 (x=0, 0.1, 0.2) hydrogen storage alloys were prepared by induction melting followed by annealing treatment. Influences of partial substitution of rare earth elements Ce, Nd and Pr for La on phase structure and electrochemical properties of (La0.7Ce0.1PrxNd2-x)(0.67)Mg0.33Ni3.0 (x=0, 0.1, 0.2) were investigated by means of X-ray diffraction (XRD), electron probe X-ray microanalysis (EPMA) and electrochemical measurements. XRD and back scattered electron images analysis shows that all of the alloys were composed of main phase with PuNi3-type structure and small amount of second phase of LaMgNi4. With the addition of the mixed rare earth elements and increasing of Pr content x, the lattice parameters c and c/a of the PuNi3-type structure increase while cell volume and a decrease. Compared with La0.67Mg0.33Ni3.0, the electrochemical properties of the (La0.7Ce0.1PrxNd2-x)(0.67)Mg0.33Ni3.0 alloys were improved obviously. Although the electrochemical capacities of the alloys decreased little compared with that of La0.67Mg0.33Ni3.0 (392.0 mAh/g), the electrode capacities became increasing (384 mAh/g) when Pr content x increased. After 100 cycles, the capacity retention rates of the electrodes increased from 64% to 82.6%-83% and the high-rate dischargeabilities (HRDs) of the alloys increased from 78.4% to 89.4%-91.1%.