Phase Structure, Electrochemical Properties and Cyclic Characteristic of a Rhombohedral-Type Single-Phase Nd₂MgNi₉Hydrogen Storage Alloy

Abstract

A single-phase PuNi3-type Nd2MgNi9 alloy was firstly prepared through induction melting followed by zoning annealing method, and the structural and electrochemical properties of the alloy were studied. Low-angle X-ray diffraction and Rietveld refinement analyses verify that the crystal structure of the Nd2MgNi9 alloy is the PuNi3-type super-stacking structure with a space group R-3m. It is found that the Nd2MgNi9 alloy electrode exhibits excellent electrochemical properties. The discharge capacity of the alloy electrode is 370.6 mAh g−1 and its high rate dischargeability reaches up to 49.6% at a 1440 mA g−1 discharge current density. Especially, the cyclic stability is heightened to 92.1% at the 100th charge/discharge cycle and retains 79% at the 300th charge/discharge cycle, which are significantly better than those of the PuNi3-type La2MgNi9 alloy. On the basis of the R-3m crystal structure calculation results, we found that the single-phase Nd2MgNi9 alloy has the smaller volume deformation rate ΔV/V (+1.19%) and lower lattice strain (0.3180(3)%) after hydrogenation/dehydrogenation, resulting in the weaker pulverization degree of the alloy particle and minor oxidization/corrosion of active material.

Self-Discharge Characteristic of La0.60Nd0.15Mg0.25Ni3.50 Alloy with Single-Phase Ce2Ni7-Type Super-Stacking Structure

“…The smaller corrosion current density means a higher corrosion resistance. 28 Based on the calculated results, the corrosion current density of the as-cast alloy, Gd 2 Co 7 and Ce 2 Ni 7 -type alloy electrodes gradually decreases and are 61.6, 60.4 and 55.4 mA cm -2 , respectively. The results show that the corrosion resistances of the three alloy electrodes are increasingly enhanced.…”

Preparation, Electrochemical Properties and Capacity Degradation Mechanism of Gd2Co7-type Superlattice Structure La0.65Gd0.10Mg0.25Ni3.50Metal Hydride Alloy

“…A 2 B 7 -type alloys are thought to have superior comprehensive electrochemical and hydrogen storage properties among the above-mentioned phases in La-Mg-Ni system, but the cycling stability still need to be enhanced for practical application. [6][7][8][9] Recently, Zhang et al 10 found that the Gd 2 Co 7 -type Sm 1.6 Mg 0.4 Ni 7 compound alloy shows high hydrogen storage capacity (1.88 wt%) and good cycling stability. The capacity retention rate of this compound reaches up to 99.3% at the 100th cycle and the crystal structure is intact even after 100 cycles.…”