Abstract
La–Mg–Ni-based superlattice structure alloys are promising negative material candidates for nickel metal hydride (Ni-MH) batteries, but their application is challenged by cycling life. Herein, we propose Sm–Mg–Ni-based alloys beyond La–Mg–Ni-based alloys to promote long-term durability. Specifically, Ce2Ni7-type single-phase Sm0.58La0.25Mg0.17Ni3.26Al0.18 and Sm0.54La0.29Mg0.17Ni3.26Al0.18 alloys have been obtained, delivering significantly high-capacity retention rates over 70 % after 500 cycles at a 1C charge and discharge rate. Furthermore, the alloy's discharge ability has been optimized via manipulating Sm/La ratios, of which its effect on the structure and electrochemical properties is detailly studied. It is found that the discharge capacity of the Sm0.58La0.25Mg0.17Ni3.26Al0.18 alloy with a higher Sm/La ratio outperforms the Sm0.54La0.29Mg0.17Ni3.26Al0.18 alloy. However, the low Sm/La ratio Sm0.54La0.29Mg0.17Ni3.26Al0.18 alloy is favorable for discharge ability at a high-rate current rate and features lower plateau pressure and enthalpy change compared with Sm0.58La0.25Mg0.17Ni3.26Al0.18. The work is expected to offer new insights into the composition design of hydrogen storage alloys with long cycling life for Ni-MH batteries.
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