Abstract：The LaMg0.25Ni4.0-xCo0.75Alx(x=0～0.3) alloys were prepared by melt spun treatment (15 m/s), and the effect of Al substitution for Ni on the phase structure and electrochemical properties of the alloys were systematically studied. The XRD analysis reveal that all the alloys are composed of La4MgNi19（A5B19 type）and LaNi5 phases. With the increasing of x value, the cell volume（V） of the two phases and the phase abundance of LaNi5 phase generally increase. The electrochemical measurements show that the increase of Al content decreases the activation properties, maximum discharge capacity and high-rate discharge ability (HRD) of the alloy electrodes, but improve the cyclic stability obviously. For example, the capacity retention rate after 100 cycles (S100) increases from 59.07% (x=0) to 85.99% (x=0.3). It is found that the decrease of maximum discharge capacity is due to the decrease of higher absorbing hydrogen phase, and the main reason for the improving cyclic life of the alloy electrodes is that the increase of Al content reduces the hydrogen absorption volume expansion rate of the particles, and decrease the internal stress caused by two kinds of hydrogen absorption phases during ab-desorbing hydrogen process, which can reduce the degrees of pulverization of alloy particles.
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