Electrochemical characteristics of La0.59Nd0.14Mg0.27Ni3.3 alloy with rhombohedral-type and hexagonal-type A2B7 phases.

A La 0.59 Nd 0.14 Mg 0.27 Ni 3.3 alloy with 72 wt% Gd 2 Co 7 -type (3R-A 2 B 7 ) and 28 wt% Ce 2 Ni 7 -type (2H-A 2 B 7 ) phases is prepared by induction melting followed by the annealing at 1148 K. Upon further increasing the annealing temperature to 1248 K, the 3R-A 2 B 7 phase transforms into the 2H-A 2 B 7 phase, forming an alloy with a 97 wt% 2H-A 2 B 7 phase and a 3 wt% 3R-A 2 B 7 phase. Electrochemical measurement shows that the discharge capacity retention of the alloy electrode at the 100 th cycle increases from 88.5% to 92.4% as the 2H-A 2 B 7 phase increases from 28 wt% to 97 wt%. Compared to the 3R-A 2 B 7 phase, the 2H-A 2 B 7 phase shows a stronger ability to resist amorphousiation during dehydrogenation and has better structural stability. Therefore, the transformation from the 3R-A 2 B 7 phase to the 2H-A 2 B 7 phase stabilizes the structure of the alloy against amorphization and oxidation, thus improving the cyclic stability of the alloy. Electrochemical pressure–composition ( P–C ) isotherms contain two discharge plateaus; the higher plateau corresponds to the 3R-A 2 B 7 phase and the lower one is associated with the 2H-A 2 B 7 phase. As the 2H-A 2 B 7 phase increases, the high-rate dischargeability of the alloy electrodes increases from 56.8% to 66.3%. [ABSTRACT FROM AUTHOR]