Effects of Cu-substitution on La0.62Ce0.38(NiCoMnAlSiZr)5.3 metal hydride alloy

• Annealing in the Nd, Pr-free AB5 alloy improves the HRD and activation.
• As Cu-amount increases in alloy, Cu occupies the B-site in the sequence 3g → 2c → 3g.
• 1% of Cu is found to have the best activation and high-rate performance.
• A stoichiometry of 5.3 in Nd, Pr-free alloy yields no B2 secondary phase.

Five Pr, Nd-free hyper-stoichiometric AB5 metal hydride alloys, having nominal alloy compositions of La9.5Ce6.4Ni69.0−xCo4.7Mn4.3Al5.7CuxZr0.1Si0.3 (x = 0, 1, 2, 3, 4) with Cu partially substituting for Ni, were prepared by induction melting. The structure, chemical composition, gaseous phase hydrogen storage properties, and electrochemical properties of these alloys were investigated. Both the as-cast and annealed (960 °C for 10 h in vacuum) alloys were made of a single CaCu5-type structure. Annealing improved the composition homogeneity, enlarged the crystallite size, and flattened the pressure-concentration-temperature isotherm. The occupancy site of Cu followed the sequence of 3g (1 at.% Cu) → 2c (2 and 3 at.% Cu) → 3g (4 at.% Cu). Improvement in activation and high-rate performance was demonstrated for the alloy containing 1 at.% Cu, but deterioration in the aforementioned properties were observed with higher Cu-content. With the incorporation of Cu, although the unit cell volume increased, both the gaseous phase and electrochemical hydrogen storage capacities decreased. 1 at.% Cu-substituted alloy showed both higher bulk diffusion constant and surface exchange current than commercially available AB5 metal hydride alloys and was recommended for high-power nickel/metal hydride battery applications.