Gas atomization of Cu-modified AB₅ metal hydride alloys

Gas atomization together with a hydrogen annealing process has been proposed as a method to achieve improved low-temperature performance of AB ₅ alloy electrodes in Ni/MH batteries and restore the original cycle life which was sacrificed by the incorporation of copper in the alloy formula. While the gas atomization process reduces the lattice constant aspect ratio c/a of the Cu-containing alloys, the addition of a hydrogen annealing step recovers this property, although it is still inferior to the conventionally prepared annealed Cu-free alloy. This observation correlates very well with the cycle life performance. In addition to extending the cycle life of the Cu-containing metal hydride electrode, processing by gas atomization with additional hydrogen annealing improves high-rate, low-temperature, and charge retention performances for both Cu-free and Cu-containing AB₅ alloys. The degradation mechanisms of alloys made by different processes through cycling are also discussed.