Microstructure and electrochemical properties of La_0.8–x MM _x Mg_0.2Ni_3.1Co_0.3Al_0.1 (x = 0, 0.1, 0.2, 0.3) alloys

The present study aims to improve electrochemical properties of the La–Mg–Ni-based hydrogen storage alloys through partial substitution for La by mischmetal (MM). The La_0.8–x MM _x Mg_0.2Ni_3.1Co_0.3Al_0.1 (x = 0, 0.1, 0.2, 0.3) alloys were prepared by inductive melting, and their phase structures and electrochemical properties were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDX) and electrochemical tests. Results show that the alloys mainly consist of La₂Ni₇-type phase, La₅Ni₁₉-type phase, LaNi₅-type phase and LaNi₃-type phase. The addition of MM does not change the phase compositions, while it leads to more uniform phase distribution and obviously promotes the formation of La₂Ni₇-type phase which possesses favorable electrochemical properties. Electrochemical studies indicate that the substitution for La by MM could effectively improve the high rate dischargeability (HRD) of the alloy electrode, and the optimal value of HRD₁₅₀₀ (HRD at 1500 mA·g⁻¹) increases from 40.63 % (x = 0) to 60.55 % (x = 0.3). Although the activation properties of the alloy electrodes keep almost unchanged, both the maximum discharge capacity (C _max) and the cycling stability are significantly improved by MM addition.