Development of Mg-Added MmNi[sub 5]-Based Alloys with Low Co Content for High Power Applications

Abstract

Mg addition effects on the structure, surface morphology, pressure-concentration-temperature properties, cyclic behavior, and high rate capability of low-Co containing mischmetal ͑Mm͒-Ni-Co-Mn-Al alloys have been investigated. The results indicated that 4 atom % Mg addition significantly improved the cycle life of this AB 5 -type alloy with low Co content. However, Mg addition caused a small decrease in the high rate capability. Pressure composition isotherm results showed that Mg addition led to an increase of plateau pressure and a loss of capacity. Scanning electron microscopy and electron probe microanalysis results showed that Mg addition resulted in some segregation of an Mg-Mn-Al phase. The decrease in the high rate capability could be attributed to the formation of the Mg-Mn-Al phase. Further results showed that the decrease of Mn/Al ratio and alkali treatment could improve the high rate capability of the Mg-added MmNi 5 -based alloys.

Stacking structures and electrode performances of rare earth–Mg–Ni-based alloys for advanced nickel–metal hydride battery

“…Average volume expansion of the alloy was estimated to be 19.7% on the basis of volume expansion ratio, mass fraction, and density of each phase. This value is much higher than that of the practi- cal MmNi 5 -based alloy (11.7%) [14], but is lower than that of LaNi 5 alloy (24.0%) [15]. Fig.…”

“…Fig. 5 shows P-C-T (pressure-composition isotherm) curves of the La 0.8 Mg 0.2 Ni 3.4−x Co 0.3 (MnAl) x alloys at 80 • C. Hydrogen storage capacity of the alloy with x = 0.4 was about H/M = 0.8, which was comparable to the conventional AB 5 -type alloys [14]. With decreasing Mn and Al content, hydrogen storage capacity increased.…”

Development of Mg-containing MmNi5-based alloys for low-cost and high-power Ni–MH battery

“…Discharge capacity of the alloy with x = 0.04 increased from 80 to 170 mAh/g. Previously, it was observed for the alloys prepared on 1 kg-batch scale that the increase in the Mg content caused the decrease in high rate capability [19]. However, this kind of behavior was not observed for …”

“…In recent years, there have been several impressive works on La-Mg-Ni alloys and related systems [15][16][17][18][19]. Kadir et al have developed AB 2 C 9 (A: rare earths, Ca; B: Mg, Ca; C: Ni)-type alloys with stacking structure consisting of AB 5 and AB 2 units [15,16].…”

“…Maeda et al reported that addition of small amount of Mg was effective to improve the cycle life of low-cobalt AB 5 -type alloy [18]. Recently, it has been shown that the Co content was successfully reduced to half of the conventional alloy (MmNi 4.0 Co 0.65 Mn 0.3 Al 0.28 ) by the addition of small amount of Mg [19].…”