A series of multicomponent Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 0.85 M 0.15 ͑M ϭ Fe, Co, Cu, Mo, and Al͒ alloys are prepared and their crystal structure and pressure-composition-temperature curves are examined. The electrochemical properties of these alloys such as discharge capacity, cycling performance, and rate capability are also investigated. Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 0.85 M 0.15 ͑M ϭ Fe, Co, Cu, Mo, and Al͒ alloys have predominantly C14 Laves phases multiple phase structure. The alloys with M ϭ Co and Fe have relatively larger hydrogen storage capacities. The discharge capacities just after activation are relatively large in the case of the alloys with M ϭ Co and Fe. They are 226 and 225 mAh/g, respectively, at the current density 60 mA/g. The Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 0.85 Co 0.15 alloy is the best one with a relatively large discharge capacity and good cycling performance. The gradual increases in the discharge capacities of the alloys with the increase in the current density ͑from 60 to 250 mA/g͒ are considered to result from the spontaneous hydrogen evolution due to an insufficient hydrogen overvoltage. During activation Ni-rich and Fe-rich regions form on the surface of the Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 0.85 Fe 0.15 alloy. They may act as active sites for the electrochemical reaction. With the increase in the number of charge/discharge cycles for the Zr 0.5 Ti 0.5 Mn 0.4 V 0.6 Ni 0.85 Fe 0.15 alloy, the quantities of the zirconium and iron dissolved in the solution increase.The nickel-metal hydride ͑Ni-MH͒ batteries using hydrogen storage alloys as negative electrodes have been developed and commercialized because they provide a high energy density, high rate capability, and long cycle life without causing environmental pollution. 1-4 AB 2 -type Zr-based Laves phase metal hydrides have been attracting much attention recently because of their larger hydrogen storage capacity and relatively longer electrochemical charge/ discharge cycle life than the commercialized AB 5 -type alloys. 5-7 Nakano et al. 8 investigated the charge/discharge characteristics and the thermodynamic properties of Zr-based AB 2 -type alloys in which Ti or Nb substituted Zr and B site was substituted partially by Ni, V, Co, Cr, Cu, Fe, etc. Ovonic Battery Company ͑OBC͒ developed Zr-Ti-V-Ni AB 2 -type alloys with relatively large discharge capacity and excellent cycling performance. 9 Lee et al. 10 investigated the electrochemical charge/discharge characteristics of Zr 1Ϫx Ti x Mn 1Ϫy V y Ni 1Ϫz M z ͑M ϭ Al, Co, Fe͒ alloys. The alloys with x ϭ 0.4-0.6 showed better cycling performance than those with x Ͻ 0.4. Choi et al. 11 reported that the discharge capacity and the activation property of Ti 0.6 Zr 0.4 V 0.6 Mn 0.4 Ni 1.0 alloy were improved by varying the contents of V and Mn and its cycling performance was improved by substituting Cr for a part of V and Ni. Kim et al. 12 developed an AB 2 -type Zr-based Laves phase alloy with high discharge capacity and high rate capability.In our previous work, 13 we studied the electrochem...

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For the syntheses of LiNi 1-y Fe y O 2 (0.000 B y B 0.300), mixtures of the starting materials with the desired compositions were preheated in an air atmosphere at 400°C for 30 min and calcined in air at 700°C for 48 h. The phases appearing in the intermediate reaction steps for the formation of lithium nickel oxide are deduced from the DTA analysis. XRD analysis, FE-SEM observation, FTIR analysis and electrochemical measurement were performed for the synthesized Li 1-z (Ni 1-y Fe y ) 1?z O 2 (0.000 B y B 0.300) samples. The samples of Li 1-z (Ni 1-y Fe y ) 1?z O 2 with y = 0.025 and 0.050 have higher first discharge capacities than Li 1-z (Ni 1-y Fe y ) 1?z O 2 with y = 0.000 and better or similar cycling performance at the 0.1 C rate in the voltage range of 2.7-4.2 V. Similar results have not previously been reported except for Co-substituted LiNiO 2 . The sample Li 1-z (Ni 0.975 Fe 0.025 ) 1?z O 2 has the highest first discharge capacity (176.5 mAh g -1 ). Rietveld refinement of the XRD patterns of LiNi 1-y Fe y O 2 (0.000 \ y B 0.100) from a starting structure model [Li,Ni] 3b [Li,Ni,Fe] 3a [O 2 ] 6c showed that cation disordering occurred in the samples.

The hydriding and dehydriding kinetics of Mg are reviewed. In order to improve the reaction kinetics of Mg with hydrogen, mechanically-alloyed Mg-10 wt.%Fe and Mg-10 wt.%Co mixtures are prepared and their hydrogen-storage properties are investigated. The activation of Mg-10 wt.%Fe is easier than that of Mg-10 wt.%Co. However, The hydriding rates (at 569-589 K, 7-11 bar I-t2) and dehydriding rates (at 589 K, 1.0 bar H2) of the mechanically-alloyed Mg-lOwt.%Co are higher than those of the mechanically-alloyed Mg-10 wt.%Fe after activation. The H~ value of Mg-10 wt.%Co after 60 rain is 3.08 wt.% at 589 K under ll bar H2 and its Ha value after 60 min is 1.48wt.% at 589 K under 1.0 bar 1-12. Mg-10wt.%Co has a smaller particle size than has Mg-10 wt.%Fe after hydriding and dehydriding cycling. The mechanical alloying of Mg with Fe and Co and the hydriding-dehydriding cycling increased the hydriding and dehydriding rates by facilitating nucleation (by creating defects on the surface of the Mg particle and by the additive) and by shortening the diffusion distances (by reducing the Mg particle sizes),

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