Pressure composition isotherms, crystal structures and electrochemical capacities of MmB5 alloy-hydrogen systems have been investigated, where Mm represents La-rich mischmetals and B5 take a composition of Ni3.8Co0.5Mn0.4Al0.3. All these multicomponent alloys belong to CaCu5-type hexagonal crystal structuxe. The volume of unit cell (or say,the interstitial hole size) becomes larger with increasing of La content and decreasing of Ce content in Mm. The larger interstitial hole leads to a decrease of dissociation pressure of their hydride, hence improves the stability of MmB5H6 and the electrochendcal capacity of the MmB5 alloy. The expansion ratio of the MmB5 for hydrogen absorption was obviously smaner than that of LaNi5 alloy. For MmB5 alloy, especially with high content of La in Mm, a lot of properties for the application in MH/Ni battery, such as against pulverization, long cycle lifetime etc can be promoted.
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