Comparison among Constituent Phases in Superlattice Metal Hydride Alloys for Battery Applications

Resumen

The effects of seven constituent phases?CeNi₃, NdNi₃, Nd₂Ni₇, Pr₂Ni₇, Sm₅Ni₁₉, Nd₅Co₁₉, and CaCu₅?on the gaseous phase and electrochemical characteristics of a superlattice metal hydride alloy made by induction melting with a composition of Sm₁₄La_5.7Mg_4.0Ni₇₃Al_3.3 were studied through a series of annealing experiments. With an increase in annealing temperature, the abundance of non-superlattice CaCu₅ phase first decreases and then increases, which is opposite to the phase abundance evolution of Nd₂Ni₇?the phase with the best electrochemical performance. The optimal annealing condition for the composition in this study is 920 °C for 5 h. Extensive correlation studies reveal that the A₂B₇ phase demonstrates higher gaseous phase hydrogen storage and electrochemical discharge capacities and better battery performance in high-rate dischargeability, charge retention, and cycle life. Moreover, the hexagonal stacking structure is found to be more favorable than the rhombohedral structure.