Structures and electrochemical cycle stability of La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.4) alloys prepared by melt spinning

In order to improve the electrochemical cycle stability of the La–Mg–Ni system A2B7-type electrode alloys, La in the alloy was partially substituted by Pr and the melt spinning technology was used for preparing La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures and electrochemical performances of the as-cast and spun alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and spun alloys have a multiphase structure which consists of two main phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The substitution of Pr for La leads to an obvious increase of the (La, Mg)Ni3 phase and a decrease of the LaNi5 phase in the alloys. The results of the electrochemical measurement indicate that the cycle stability of the alloy monotonously rises with increasing Pr content. When Pr content rises from 0 to 0.4, the capacity retaining rate after 100 cycles increases from 65.32 to 79.36% for the as-cast alloy, and from 73.97 to 93.08% for as-spun (20 m s−1) alloy. The melt spinning significantly improves the cycle stability of the alloys. When the spinning rate grows from 0 (as-cast was defined as spinning rate of 0 m s−1) to 20 m s−1, the capacity retaining rate after 100 cycles increases from 65.32 to 73.97% for the (x = 0) alloy, and from 79.36 to 93.08% for the (x = 0.4) alloy.