Electrochemical study of intermetallic metal hydride as an anode material for Ni–MH batteries

The electrochemical behavior of Cobalt-free LaNi_3.55Mn_0.4Al_0.3Co_0.4Fe_0.35 alloy electrode in alkaline solution was investigated using electrochemical impedance spectroscopy (EIS) at different number of charge/discharge cycles. A physicochemical model is developed in order to simulate impedance data. Kinetic parameters are obtained by fitting the electrochemical impedance spectrum performed at different number of cycles. The charge-transfer resistance decreases with increasing number of charge/discharge of cycles, whereas exchange current density and hydrogen diffusion coefficient parameters increase with increasing number of cycles. In addition, the specific surface area of LaNi_3.55Mn_0.4Al_0.3Co_0.4Fe_0.35 alloy electrode increases due to pulverization and the formation of new active sites during charge/discharge cycling. The results of EIS measurements indicate that the performance of the LaNi_3.55Mn_0.4Al_0.3Co_0.4Fe_0.35 metal hydride electrode was markedly improved with increasing number of cycles which is mainly attributed to the increase in the reaction surface area and the improvement in the electrode surface activation.