Study On The Structure And Electrochcmical Properties Of La-Mg-ni-based Hydrogen Storage Clcctrode Alloys

Based on the review of the research and development of the La-Mg-Ni based hydrogenstorage alloys, a series of as-cast and as-spun alloys were prepared with the help of the25kg-grade vacuum medium-frequency induction melting furnace. Then, the effects ofpreparing method, annealing treatment and alloy composition on structure andelectrochemical properties of these alloys were investigated respectively. The as-cast andas-spun La_0.92Mg_0.08Ni_3.53Co_0.65alloys, the as-cast La0.9Mg0.1Ni3.4Co0.6alloy with differentannealing temperature and annealing time and the （La,Mg）（Ni,Co,Al）y（y=4.45,4.16,4.15,4.1）alloys, the （La,Mg）（Ni,Co）y（y=4.2,4.0,3.8） alloys were discussed in detail, and the effect ofthe content of Al and Co on the La_0.92Mg_0.08（Ni3.12CoxAly）4.1（x=0.60,y=0.38;x=0.66,y=0.32）alloy has also been studied. This work completed mainly by means of the XRD analysis andthe galvanostatic charge-discharge electrochemical test method.The as-cast and as-spun La_0.92Mg_0.08Ni_3.53Co_0.65alloys were mainly composed of theLaNi₅phase and the La₂Ni₇phase, but the phase abundance of the former is higher than thelatter. And the phase abundance of the LaNi₅phase of the as-cast alloy is higher than that onthe as-spun alloy, while the phase abundance of the La₂Ni₇phase is just on the opposite. Thecell volume of the LaNi₅phase of the as-cast alloy is bigger than that of the as-spun alloy andthe cell volume of the La₂Ni₇phase is on the opposite too. The result shows that the as-castLa_0.92Mg_0.08Ni_3.53Co_0.65alloy has a much better overall electrochemical properties then theas-spun alloy.As for the La_0.90Mg_0.10Ni_3.45Co_0.65alloy, heat treatment can change the phase abundanceand cell volumes. Both the lattice parameters and cell volumes of the phases, saying the LaNi₅phase and the La₂Ni₇phase, increase firstly and then decrease with the increasing annealingtemperature, and the annealing time achieves the same result. But the phase abundance ofthese two phases varies differently. We also notice that the expansion of the unit cells isisotropic.The alloy composition has a much greater effect on the structure and electrochemicalproperties of the La-Mg-Ni based hydrogen storage alloy than any other factors. As for thiskind of alloy, the content of Mg should not be too low, especially when the B/A ratio is closeto5, or it will work like an AB5-type alloy. The substitution of Al for Co can be favorable fora better cyclic stability of the alloy owing to the improvement of the corrosion resistance inthe alkaline electrolyte, though at a cost of its capacity.