Abstract:

Pressure composition isotherms, crystal structures and electrochemical capacities of MmB_5 alloy-hydrogen systems have been investigated, where Mm represents La-rich mischmetals and B_5 take a composition of Ni_(3.8)Co_(0.5)Mn_(0.4)Al_(0.3). All these multicomponent alloys belong to CaCu_5-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 MmB_5H_6 and the electrochemical capacity of the MmB_5 alloy. The expansion ratio of the MmB_5 for hydrogen absorption was obviously smaller than that of LaNi_5 alloy. For MmB_5 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.

Key words: Metalhydride, Electrode materials, X-ray diffraction, P-C Isotherms