Effect of Al substitution on electrochemical performance of La-Mg-Ni hydrogen storage alloys

La_0.7Mg_0.3Ni_3.5-xAl_x (x=0, 0.1, 0.3, 0.7, 1.0) and La_0.7Mg_0.3 Ni_2.8Co_0.7-xAl_x (x=0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by solid diffusion reaction under Ar atmosphere. The phase structures of alloys were analyzed by X-ray diffraction (XRD), as well as the electrochemical performance of alloy electrode with cyclic voltammetry (CV)and charge/discharge test, so as to investigate the effect of Al substitution on electrode characteristics. The results show that all alloys are composed of LaNi₅, La₂Ni₇ and LaNi₃ phases. With the increase of x value, the cell volume of La₂Ni₇ phase enlarges and the content of LaNi₅ phase becomes low markedly, while the content of LaNi₃ phase increases. La₂Ni₇ phase can be favorable to improve charge/discharge properties of alloy electrode. However, excessive content of Al has a negative impact on the discharge performance of alloys. The maximum values are 354.5 mA·h/g and 373.1 mA·h/g for La_0.7Mg_0.3Ni_3.4Al_0.1 and La_0.7Mg_0.3 Ni_2.8Co_0.6Al_0.1 electrodes, respectively. Cyclic voltammetry results indicate that the significant peaks responding to oxidation and reduction reactions and small difference between peak potentials mean good reversibility of the electrode during charge/discharge reaction.