Investigations on synthesis, characterization and hydrogenation behaviour of the spin- and thermal-melted versions of LaNi5 - xSix (x = 0.1, 0.3, 0.5) hydrogen storage materials

Abstract

The present study deals with investigations on the synthesis and characterisation of negative electrode material for high energy density Ni-MH battery. The hydrogen storage material (MH) has been synthesised through normal casting and melt-spinning techniques. In LaNi5/MmNi5 family various substitutions like Al, Mn, Co have been studied. The substitution of metalloid like Si is known to be very helpful in improving several hydrogenation properties. In the present study, the Si substituted versions of AB5-type storage materials typified by LaNi5 - xSix (x = 0.1,0.3,0.5) have been investigated. A comparison between the present material and the conventional AB5-type material MmNi4.3Al0.3Mn0.4 has also been made which has been previously studied. The main features revealed by XRD characterisations are the existence of the free Ni and Si together with AB5 material for all the three compositions. These free Ni and Si were found to disappear and yield, giving rise to a singular material after hydrogenation. The melt-spun version of the material was found to grow invariably in a direction perpendicular to the c-axis. The kinetics and activation process was better for the melt-spun version of the LaNi4.7Si0.3 alloy than its thermally-melted counterpart (bulk) as well as to the alloy MmNi4.3Al0.3Mn0.4. For example, the kinetics of the melt-spun version of LaNi4.7Si0.3 is 60% faster than its bulk version and 70% faster than the melt-spun version of MmNi4.3Al0.3Mn0.4. Similarly, the melt-spun version of the alloy LaNi4.7Si0.3 gets activated in the 2nd cycle itself where as the alloy MmNi4.3Al0.3Mn0.4 attains this stage only in the 6th cycle. © 1998 Elsevier Science S.A.