EFFECT OF SILICON ON THE PROPERTIES OF AB5-BASED ALLOYS FOR BATTERY ELECTRODE APPLICATION

Because of their rather low hydrogen storage capacity LaNi5-xSix-alloys have not been studied and have not been considered for battery applications so far. We have found, however, that the alloy LaNi4.5Si0.5 shows fast activation and incredibly high stability upon electrochemical cycling (-0.07 mAh/g/cycle) with fairly high electrochemical capacity (245 mAh/g). This positive effect of silicon was also found in combination with aluminium in (La,Lm,Mm)(Ni,Si,Al)5 alloys where, however, the hydrogen storage capacity was quite low. Heat treatments of LaNi4.7Si0.3 showed only minor effects on the cyclic stability. PCT, XPS and electrochemical measurements were carried out on (La,Lm,Mm)(Ni,Si,Al)5 alloys. Electrochemical cycling in 6 M KOH electrolyte forms a sublayer rich in metallic nickel the rare earth probably beeing dissolved in the electrolyte. Contrary to earlier suggestions no passivating silicon or aluminium surface oxide film could be found on cycled electrodes.