A new choice for the anode of nickel metal hydride batteries with long cycling life: A Ce2Ni7-type single-phase Nd0.80Mg0.20Ni3.58 hydrogen storage alloy

Abstract

RE–Mg–Ni-based superlattice alloys with superior discharge capacity are deemed as alternatives of commercial AB5-type alloys for the anode of nickel metal hydride batteries, however, their application is plagued with the inadequate cycle life. Here we report a Ce2Ni7-type single-phase Nd0.80Mg0.20Ni3.58 alloy for electrochemical hydrogen storage with an ultra-high cycling stability, which offers a capacity retention of 94.7% over 100 cycles and cycles over 360 times as reaching 80% of its maximum discharge capacity. The alloy with the specific Ce2Ni7-type single phase is prepared by the zoning annealing treatment of as-cast ones based on peritectic reactions, where minor CaCu5-, MgCu4Sn- and Ce5Co19-type phases in the as-cast alloy convert to the Ce2Ni7-type phase in a temperature range of 950–985 °C, a Gd2Co7-type phase in the as-cast alloy constantly transforms into the Ce2Ni7-type phase within another 105 °C higher, and the single phase maintains its stability from 1100 to 1130 °C. We find the superior cycling stability of the single-phase alloy benefits from the stable crystal structure, weak pulverization, and suppressive oxidation/corrosion of active elements owing to a compactly covered Nd(OH)3 on the surface of the alloy. These findings will promote the development of the long-life nickel metal hydride batteries.