Preparation of Mg_2-xRE_xNi (RE = La, Ce, Pr, Nd, Y) alloys and their electrochemical characteristics

A series of Mg_2-xNd_xNi (x=0.05, 0.1, 0.2, 0.3) and Mg_1.95RE_0.05Ni (RE=La, Ce, Pr, Nd, Y) ternary alloys were prepared by ball milling of mixed powder of Mg, Ni, RE and sintering under pure argon. XRD analysis shows that Mg_2-xNd_xNi (x=0.05, 0.1) and Mg_1.95RE_0.05Ni alloys are all single-phase with the same crystal structure as Mg₂Ni while three phases (including Mg ₂Ni, NdNi and NdMgNi₄) were formed in Mg _1.8Nd_0.2Ni and Mg_1.7Nd_0.3Ni alloys. The lattice constants (a, c, c/a) of Mg₂Ni phase in these ternary alloys were calculated. Calculated values of a and c are strongly influenced by elemental substitution, while no different changes were observed in a/c. The electrochemical characteristics of the alloys were evaluated by simulated battery test. It is found that the initial discharge capacity of Mg _2-xNd_xNi alloy milled for 10h was obviously improved with increasing Nd content. A good cycle life was also observed in the Mg _1.7Nd_0.3Ni alloy electrode. It is suggested that combined effects contribute to the enhancement in electrochemical characteristics, the presence of NdMgNi₄ being beneficial for the improvement in cycle life of Mg_2-xNd_xNi (x=0.2, 0.3), especially for the Mg_1.7Nd_0.3Ni alloy electrode. As to Mg _2-xRE_xNi alloys, the effectiveness in improving the discharge capacity increased in the following order: Pr>Nd>Ce>La>Y.