An Investigation On Structural And Electrochemical Properties Of La₁₅Fe_77-xNi_xMn₅B₃(x=55,60,65,70,75) Hydrogen Storage Alloys

Hydrogen storage alloy is a kind of material that is capable of storing mass hydrogen atom in crystal voids. The hydrogen storage density per unit volume of the alloy exceeds the density of liquid hydrogen and solid hydrogen. Besides, the operation is easy and safe. To obtain new La-Fe-B series hydrogen storage alloy with high capacity, low cost and good high rate discharge (HRD) properties, the La15Fe77_xNixMn5B3 (x=55,60,65,70,75) hydrogen storage electrode alloys were prepared by vacuum melting and rapid quenching method. In this paper, influence of partial substitution of Ni for Fe and quenching treatment on the electrochemical properties and alloy structural was systematically investigated by XRD, SEM and EDS, and electrochemical test.The results show that all alloys were composed of LaNi5, La3Ni13B2 and (Fe, Ni) phases. Electrochemical test indicates that the plateau region of the hydrogen desorption becomes wider and flater with increasing Ni content. These alloys can be easily activated within 2 cycles when x≥70. The maximum discharge capacity (Cmax) of the alloy electrodes gradually increased from 222mAh-g-1 (x=55) to 309mAh-g-1(x=75) with increasing x. The high rate dischargeability (HRD) of the alloy electrodes was significantly improved as the Ni content of the alloys increases, such as the HRD with discharge current density Id=1750mA.g-1 increases from 14.3 (x=55) to 86.7%(x=75). However, the cycling life of the alloy electrodes gradually decreases with decreasing Fe content.The composition of alloy became homogeneous after quenching treatment. At the same time, the plateau region of the desorption P-C isotherm of the alloy was flattened and the desorption plateau pressure reduced. Quenching treatment improved activation characteristics, discharge capacity, and HRD of alloy electrode. However, cycling stability of alloy electrode was deteriorated by quenching treatment.