A new strategy for enhancing the cycling stability of superlattice hydrogen storage alloys

Abstract Superlattice hydrogen storage alloys are one of the most potential candidates for the negative electrode materials of nickel-metal hydride batteries. However, their crystal structure damage and oxidation/corrosion during battery cycling severely deteriorate their cycle life. In this work, we propose a new strategy based on the alloys’ structure characteristics analysis and First-principles calculation to enhance their cycling stability. The strategy equalizes the sublattice volumes of [A2B4] and [AB5] by atomic selective occupation and meanwhile increases the alloys’ electronegativity. The feasibility of the strategy is validated experimentally by designing a series of single-phase superlattice alloys with simple elemental compositions of La0.75-xGdxMg0.25Ni3.5 (x = 0, 0.05, 0.1, 0.15). It is found that when appropriate amount of Gd is added, the sublattice volumes of [LaMgNi4] and [LaNi5] become equal, so that the alloy maintains a stable crystal structure in the long-term battery cycling. Moreover, the alloys’ oxidation/corrosion resistance is enhanced due to the high electronegativity of Gd. The alloys’ capacity retention after 100 cycles is improved from 82.1% (La0.75Mg0.25Ni3.5) to 88.2% (La0.60Gd0.15Mg0.25Ni3.5) without sacrificing the maximum discharge capacity, and meanwhile the high rate dischargeability is also increased. The design strategy provides new insights for overcoming the weakness in the cycling stability of superlattice hydrogen storage alloys, thus promoting their practical applications.