Effect of Al content on the structural and electrochemical properties of A2B7 type La–Y–Ni based hydrogen storage alloy

LaY1.9Ni10.2−xAlxMn0.5 (x = 0–0.6) hydrogen storage alloys have been prepared using a vacuum induction-quenching furnace and annealed at 1148 K for 16 h. The alloys are composed of Ce2Ni7- and Gd2Co7-type phases and an extra Pr5Co19-type phase appears when x = 0.6. Aluminum tends to enter the inner AB5 slabs of Ce2Ni7- and Gd2Co7-type phases and promotes the generation of new AB5 slabs. The maximum discharge capacity of the alloy electrodes is stable at approximate 375 mA h/g as x increases from 0 to 0.4 and then decreases to 364.2 mA h/g (x = 0.6). The cycling capacity retention rate at the 300th cycle is 59.4%, 62.0%, 62.7% and 58.7% for x = 0, 0.2, 0.4 and 0.6, respectively, indicating that the function of aluminum on improving the cyclic stability of the alloy electrodes is limited. The main reason is that the similar pulverization degrees of the alloys are presented during the charge/discharge cycles.