The role of microcracking in ZrCrNi hydride electrodes

As-cast ZrCrNi was found to exhibit high capacities and good cycle life when used as a hydride electrode in nickel/metal hydride batteries, but was extremely slow to activate. As-cast ZrCrNi was found to be comprised of a primary C14 Laves phase with a uniformly dispersed second phase of Zr7Ni10. When annealed to a single C14 phase, ZrCrNi delivered virtually no capacity. Microscopic studies of activated and unactivated material suggests that the key activation mechanism is the formation of a ubiquitous network of microcracks. A model is proposed to explain the formation of the microcracks and their role in activation. It is further shown that activation can be greatly accelerated by a pulse activation process.