Structure and electrochemical properties of La_1−xMg_xNi_2.8Co_0.4Mn_0.1Al_0.2 (x = 0.25, 0.30, 0.33) hydrogen storage alloys

La_1−xMg_xNi_2.8Co_0.4Mn_0.1Al_0.2 (x = 0.25, 0.30, 0.33) alloys were prepared by induction melting followed by annealing treatments (1,073 K) for 10 h. The structure and electrochemical properties of La_1−xMg_xNi_2.8Co_0.4Mn_0.1Al_0.2 (x = 0.25, 0.30, 0.33) hydrogen storage alloys were investigated by X-ray powder diffraction (XRD) and electrochemical measurement methods. XRD results reveal that all the alloys mainly consist of LaNi₅ phase and La₂Ni₇ phase. The electrochemical experiments demonstrate that the substitution of Mg for La can increase the maximum discharge capacity and improve the high-rate dischargeability of the alloy electrodes. The high-rate dischargeability of alloy electrodes increases from 39.4 % to 63.1 % with x increasing from 0.25 to 0.33 at discharge current density of 1,500 mA·g⁻¹. However, the addition of Mg reduces the cycling stability of the electrodes. Furthermore, the results obtained from the electrochemical impedance spectroscopy and linear polarization measurements show that the hydriding kinetics on the hydrogen storage alloys are controlled by charge-transfer step.