Effect of Ce, Co, and Sn Substitution on Gas Phase and Electrochemical Hydriding/Dehydriding Properties of LaNi5

Abstract

A number of LaNis-based intermetallics with Ce, Sn, and Co substitutions were prepared by the arc-melting technique and tested as electrodes in Ni/MHx batteries. Sn and Co substitution expand the unit cell and lower the plateau pressures whereas the introduction of Ce results in the reverse effects. Ce and Co substitutions result in a decrease in the storage capacity of the intermetallics. Most of the Sn substituted compounds exhibit high hydriding capacities, though they widely differ in their electrochemical behavior, viz., cycle life and rate capabilities. Two such intermetallic compounds, with different amounts of substitution, show promise with high capacities (over 300 mAh/g), even at high rates of discharge. Intermetallics with Ce, Sn, and Co retain the high capacity upon long-term cycling.

Electrochemical performance of LaNi5−xSnx alloys

“…Table 1 lists the crystal structure data. As reported [2,3], partial substitution of Sn for Ni in LaNi 5 results in a considerable lattice expansion, which is attributed to the substitution of the larger atoms Sn for Ni.…”

“…1. discharge rate, this alloy reaches its largest discharge capacities of about 300 mAh, which is almost the same performance as reached with several other substituents together. For example, it was reported that the initial discharge capacity of La 0.8 Ce 0.2 Ni 4.8 Sn 0.25 , LaNi 4.25 Co 0.5 Sn 0.25 , La 0.8 Ce 0.2 Ni 3.5 Co 1.2 Sn 0.25 and La 0.8 Ce 0.2 Ni 4.25 Co 0.5 Sn 0.25 is 315, 320, 265 and 309 mAh at 0.5C rate, respectively [2]. Even at large rates such as at 480 mA/g charge and 500 mA/g discharge rate (Fig.…”

“…It can be seen that most of LaNi 5−x Sn x alloys can be activated in three to four cycles. (2) The electrochemical effect of Sn on LaNi 5 is not linear. That means the electrochemical performance of LaNi 5−x Sn x does not change linearly with the value of x.…”

“…A small-unoptimized amount of Sn LaNi 4.8 Sn 0.2 stabilizes the MH-alloy almost to the same degree as several other substituents together [1,2]. Lambert et al found that Sn substituted alloys show no X-ray line broadening and little capacity decay even after 10,000 thermal cycles [3].…”

Investigation of a Novel Metal Hydride Electrode for Ni-Mh Batteries

“…The maximum electrochemical capacity experimentally observed was 338 mAh/g for ZrMn0.5V0.5Ni1.4, and the discharge efficiency was found to be 85%. Hence the fundamental studies on the charge/discharge characteristics are required for improving the performance of a Ni-MH battery 9,10 . The present work focuses on elucidating the electrochemical properties on AB2 alloy with the composition YxZr1-xMnmFenCopVoCrq (m+n+o+p+q=2) and the processes that occur during charge and discharge and the rate of diffusion of hydrogen in the electrode has also been presented.…”