Effects of alloying elements and binder on the electrochemical behavior of metal hydride electrodes in potassium hydroxide electrolyte

This investigation examines the effect of alloying elements on the charge-discharge performance of LaNi_3.6(Co + Mn+Al)_1.4 electrodes in 7 M KOH electrolyte. The activation behavior and the effect of binder content were also examined. Both half-cell and full-cell systems were employed to evaluate the electrochemical performance. Experimental results indicated that a few cycles of charge-discharge at a rate of 150 mA/g in 7 M KOH electrolyte were sufficient to activate the freshly prepared LaNi _3.6(Co + Mn + Al)_1.4 electrodes. The amount of binder affected the activation behavior, the overvoltage for hydrogen ions reduction and the discharge capacity of the MmNi_3.55 Co_0.75Mn _0.4Al_0.3 electrode. In the alloy of the LaNi _3.6 (Co + Mn + Al)_1.4 electrodes, a high Co content helped to promote both the capacity at a relatively low discharging rate and the cyclic life. An increase of the Al content raised the discharge voltage and improved the high rate discharge capacity, but reduced the cyclic stability. The alloy with a high Mn content required the least cathodic polarization during charging but had the lowest discharge capacity at a rather high discharging rate.