Microstructures and electrochemical properties of Co-free AB₅-type hydrogen storage alloys through substitution of Ni by Fe

The structure and electrochemical properties of a cobalt-free hydrogen storage electrode alloy LaNi_4.05-xAl_0.45Mn_0.5Fe_x (0 ≤ x ≤ 0.5) have been investigated with different additions of Fe in replacement of Ni. With the increase of Fe content the maximum discharge capacity gradually decreases from 334.8 mAh g^-1 to 292.8 mAh g^-1, however the cycle stability is improved correspondingly. The capacity decay can remain 28.6% (x = 0.5) after 300 charge/discharge cycles. The high rate discharge (HRD) ability of the alloys (x ≤ 0.5) is improved with the increase of Fe content. It is found that all of the alloys are single CaCu₅ phase structure disclosed by XRD pattern. However, small amount of the La₂O₃ phase, observed from SEM photographs, exists on the matrix of all the alloys and when x = 0.5, some web-like LaNi_2.28 phase is segregated out along the crystal boundary.