Magnesium influence in the electrochemical properties of La–Ni base alloy for Ni–MH batteries

Abstract

The effect of the substitution of La by Mg in the hypo-stoichiometric La 1 - x Mg x Ni 3.8 Co 0.3 Mn 0.3 Al 0.4 ( x = 0.00 , 0.05, 0.10, 0.15 and 0.20) hydride alloys were metallurgically and electrochemically characterized in order to use them as negative electrodes in Ni–MH batteries. The Mg content was added to mother alloys by means of low energy mechanical alloying. The microstructure, composition and crystalline structure of the samples were analyzed by SEM, EDS and X-ray diffraction, respectively, and their electrochemical properties were analyzed by charge/discharge cycling stability and rate capability. The electrochemical results show that the alloy LaNi 3.8 Co 0.3 Mn 0.3 Al 0.4 reaches a maximum discharge capacity of 181.7 mAh/g. La 0.85 Mg 0.15 Ni 3.8 Co 0.3 Mn 0.3 Al 0.4 presents the best behavior in electrochemical cycling stability with a capacity decay of 4.4% after 50 cycles and a capacity reduction rate of 0.117 mAh/g per cycle. The alloy La 0.80 Mg 0.20 Ni 3.8 Co 0.3 Mn 0.3 Al 0.4 obtained the highest discharge capacity at high rate discharge.