Effects of annealing treatment on the microstructure and electrochemical properties of low-Co hydrogen storage alloys containing Cu and Fe

Abstract

The effects of annealing treatment on the microstructure and electrochemical properties of low-Co LaNi 3.55 Mn 0.35 Co 0.20 Al 0.20 Cu 0.75 Fe 0.10 hydrogen storage alloys were investigated. X-ray diffraction (XRD) analysis indicated that annealing treatment remarkably reduced the lattice strain and defects, and increased the unit-cell volume. The optical microscope analysis showed that the as-cast alloy had a crass dendrite microstructure with noticeable composition segregation, which gradually disappeared with increasing annealing temperature, and the microstructure changed to an equiaxed structure after annealing the alloy at 1233 K. The electrochemical tests indicated that the annealed alloys demonstrated much better cycling stability compared with the as-cast one. The capacity retention at the 100th cycle increased from 90.0% (as-cast) to 94.7% (1273 K). The annealing treatment also improved the discharge capacity. However, the high rate dischargeability (HRD) value of the annealed alloy slightly dropped, which was believed to be ascribed to the decreased exchange current density and the hydrogen diffusion coefficient in alloy bulk.

The Current Status of Hydrogen Storage Alloy Development for Electrochemical Applications

“…Properties of the La-Pr-Nd group fall between the properties for La- and Nd-only alloys. Annealing is the most convenient method to manipulate phase distribution, and its effect was reported on La-only [107,108,109,110,111,112,113], Nd-only [24], La-Gd [114], La-Nd [115], La-Pr-Nd [116,117], and La-Ce-Pr-Nd [118] alloys. While Nd-only and La-Pr-Nd superlattice alloys are used in low self-discharge and high capacity NiMH batteries, respectively, La-only superlattice alloy is not used in commercial products due to its low cycle life from pulverization [119].…”

Study on the microstructure and electrochemical kinetic properties of MmNi4.50−xMnxCo0.45Al0.30 (0.25≤x≤0.45) hydrogen storage alloys

“…A great amount of investigations, such as elemental substitution [1][2][3], heat treatment [4,5] and surface treatment [6][7][8] have been carried out on AB 5 -type hydrogen storage alloys to improve the electrochemical properties. The chemical compositions contribute to phase structure and corresponding electrochemical properties.…”