Effect of Temperature on Structure and Electrode Properties of LaNi3.8Co0.6Mn0.3M0.3 Hydrogen Storage Alloys

A series of experiments have been performed to investigate the temperature effects on the structure and the electrochemical properties of LaNi3.8Co0.6Mn0.3M0.3 (M=Ni, Al, Cu) hydrogen storage alloys at different temperatures of 238, 273, 303 and 323 K. Samples A, B and C were used to represent LaNi4.1Co0.6Mn0.3 (Ni substituted alloy), LaNi3.8Co0.6Mn0.3Al0.3 (Al substituted alloy) and LaNi3.8Co0.6Mn0.3Cu0.3 (Cu substituted alloy), respectively. The structures and the electrochemical properties of A, B and C hydrogen storage alloys were investigated by XRD and simulated battery test, respectively. The results reveal that all of the alloys are composed of the homogeneous LaNi5 phase with a CaCu5-type hexagonal structure. The low-temperature properties of the Cu substituted alloy are improved, and the high-temperature discharge capacity of the Al substituted alloy is enhanced. Electrochemical impedance spectroscopy (EIS) analysis shows that the improvement of high-temperature discharge capacity of alloy electrode B is attributed to the formation of dense oxide film to protect the active material from corrosion, which is not favorable to charge-transfer reaction at the interface of electrode-electrolyte. The deterioration in the high-rate dischargeability (HRD) of alloy electrodes B and C are attributed to the degradation of electrochemical kinetics, including both charge-transfer reactions on the electrode surface and hydrogen diffusion in the bulk. Furthermore, the good low-temperature performance of alloy electrode C is due to the improvement of charge-transfer reaction.