Structures and Electrochemical Hydrogen Storage Properties of the As-Spun RE-Mg-Ni-Co-Al-Based AB₂-Type Alloys Applied to Ni-MH Battery

In this paper, the La_0.8−x Ce_0.2Y _x MgNi_3.5Co_0.4Al_0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) alloys were synthesized via smelting and melt spinning. The effect of Y content on the structure and electrochemical hydrogen storage characteristics of the as-cast and spun alloys was investigated. The identifications of XRD and SEM demonstrate that the experimental alloys possess a major phase LaMgNi₄ and a minor phase LaNi₅. The variation of Y content results in an obvious transformation of the phase abundance rather than phase composition in the alloys, namely LaMgNi₄ phase increases while LaNi₅ phase decreases with Y content growing. Furthermore, the replacement of Y for La causes the lattice constants and cell volume to clearly decrease and markedly refines the alloy grains. The electrochemical tests reveal that these alloys can obtain the maximum values of discharge capacity at the first cycling without any activation needed. With Y content growing, the discharge capacity of the alloys obviously declines, but its cycle stability remarkably improves. Moreover, the electrochemical dynamics of the alloys, involving the high-rate discharge ability, hydrogen diffusion coefficient (D), limiting current density (I _L), and charge transfer rate, initially augment and then decrease with rising Y content.