Influences Of Stoichiometry On The Phase Structure And Electrochemical Properties Of AB₅ Hydrogen Storage Alloys

The paper intents to get hydrogen stotage alloys with good synthetical properties through using non-stoichiometic methods. The phase structure and electrochemical properties of alloys were systematically investigated by means of X-ray diffraction, metallography, SEM, electrochemical methods. Losing efficiency of storaging hydrogen alloys electrodes was studied. The results were as follows:In A kind of as-cast alloys, main phases of the other alloys are CaCu5-type structure LaNi5 phase, except x=3. 8 with more LaNi3 phase. The alloys consisted of LaNi3 secondary phase with x=4.4—5.2, and the amount of the second phase decreased with the increasing of stoichiometric ratio x, the alloy with x=5. 4 segregated rich-Ni phase. Activity of the alloys was favorable with x=4. 4~ 5.4. Discharge capacity , high-rate discharge capability, cycling stability as well as discharge voltage character of over- stoichiometric were enhanced, and synthetical properties were reduced with x increasing to 5.8.In B kind of as-cast alloys, main phase of alloys were all CaCus-type structure, x=4.8, x=5.0, x=5. 2 of alloys consisted of LaNi second phase, and the alloys with 4.8≤x≤5.2, the amount of the second phase decrease with the increasing of x. Maximum discharge capacity , high-rate discharge capability ^ cycling stability of over-stoichiometric were enhanced. A partial substitution of Co by a small amount of Cu, Fe, Si, Cr was favorable in improving synthetical properties, especially improving cycling stability.Melt-spun alloys have low activation performance and discharge capacity , but their cycling stability were good.Decay process of hydrogen storage alloys was as follows: charging and discharging hydrogen→grains pulverized→ grains mini shed→ bigger active surface contacted with electrolyte → grains surface oxidated→ losing of active substance increased→discharge capacity decreased.