Effects of Rapid Quenching on the Microstructure and Electrochemical Characteristics of La0.7Mg0.3Co0.45Ni2.55−xCux(x=0−0.4) Electrode Alloys

The hydrogen storage alloys La0.7Mg0.3Co0.45Ni2.55-xCux (x = 0, 0.1, 0.2, 0.3, 0.4) were prepared by casting and rapid quenching. The effects of the rapid quenching on the microstructures and electrochemical performances of the specimen alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure, including the (La, Mg)Ni3 phase, the LaNi5 phase and the LaNi2 phase. The rapid quenching has no much influence on the phase compositions of the alloys, but it obviously changes the phase abundances of the alloys. The rapid quenching can significantly improve the composition homogeneity of the alloys and markedly decrease the grain size of the alloys. The results obtained by the electrochemical measurement indicate that the rapid quenching obviously enhances the cycle stability of the alloys, but it decreases the discharge capacity and the activation capability of the alloys. The rapid quenching has an obvious influence on the discharge potential of the alloys. When the quenching rate was larger than 15 m/s, it clearly decreased the discharge plateau potential and increased the slopes of the discharge potential plateaus of the alloys.