Synthesis and characterization of metal hydride electrodes. Interim report

The objective of this project is to elucidate the compositional and structural parameters that affect the thermodynamics, kinetics and stability of alloy hydride electrodes and to use this information in the development of new high capacity long life hydride electrodes for rechargeable batteries. The work focuses on the development of AB{sub 5} alloys and the application of in situ methods, at NSLS, such as x-ray absorption (XAS), to elucidate the role of the alloying elements in hydrogen storage and corrosion inhibition. The most significant results to date are: The decay of electrode capacity on cycling was directly related to alloy corrosion. The rate of corrosion depended in part on both the alloy composition and the partial molar volume of hydrogen, V{sub H}. The corrosion rate depended on the composition of the A component in AB{sub 5} (LaNi{sub 5} type) alloys. Partial substitution of La with Ce in AB{sub 5} alloys substantially inhibits electrode corrosion on cycling. Recent results indicate that Co also greatly inhibits electrode corrosion, possibly by minimizing V{sub H}. The AB{sub 5} alloys investigated included LaNi{sub 5}, ternary alloys (e.g. LaN{sub 4.8}Sn{sub 0.2} and La{sub 0.8}Ce{sub 0.2}Ni{sub 5}), alloys with various substitutions for both La and Ni (e.g. La{sub 0.8}Ce{sub 0.2}Ni{sub 4.8}Sn{sub 0.2}) and mischmetal (Mm) alloys of the type normally used in batteries, such as MmB{sub 5} (B = Ni{sub 3.55}Mn{sub 0.4}A1{sub 0.3}Co{sub 0.75}). A major effort was devoted to the effects of La substitution in the A component. Both in situ and ex situ XAS measurements are used to study the electronic effects that occur on the addition of various metal substitutions and on the ingress of hydrogen