Effect of Al and W substitution for Ni on the microstructure and electrochemical properties of La_1.3 CaMg_0.7 Ni_{9 - x} (Al_0.5 W_0.5)_x hydrogen storage alloys

The microstructure and electrochemical properties of La_1.3 CaMg_0.7 Ni_{9 - x} (Al_0.5 W_0.5)_x(x = 0, 0.3, 0.6, 0.9) hydrogen storage alloys have been studied systematically. XRD and SEM analyses show that the alloys are mainly composed of the(La, Mg) Ni₃ phase and the LaNi₅ phase, but the Al and W substitution for Ni results the disappearance of the (La, Mg)₂ Ni₇ phase and the segregation of W pure metal phase. The cell volumes of the (La, Mg) Ni₃ phase and the LaNi₅ phase increase by adding the content of Al. With increasing x, the maximum discharge capacity of the alloy electrodes decreases from 380 (x = 0.0) to 317.6 mA h/g (x = 0.9). However, cyclic stability is noticeable improved from 72.2% (x = 0.0) to 85.2% (x = 0.9) up to 100 cycles. The HRD and exchange current density I₀ of the alloy electrodes decrease first and then increase.