Electrochemical properties of a LaNi4.7Al0.3 alloy used for the negative electrode in nickel/metal hydride batteries

The electrochemical properties of an activated LaNi4.7Al0.3 hydride electrode (MH) were studied using charge/discharge and polarization tests. The rests were performed at different steady states of discharging and temperatures. Both the exchange current density (I-0) and the symmetry-factor (beta) of the MH electrode in a 6M KOH aqueous solution decrease with increasing hydrogen concentration and increase with increasing temperature at a given hydrogen concentration. These intrinsic parameters (I-0 and beta) were then used to evaluate the characteristics of the nonequilibrium discharge process of the MH electrode, including the discharge overpotential and activation. From the exchange current density measurements, the apparent activation energy (E-a) was found to be in the range 15.5 to 22.5 kJ.(molH)(-1) for hydrogen concentrations H/M=0.6 to 0.1 in the temperature range 273-318K. It is suggested that the apparent activation energy (E-a) is a useful intrinsic parameter for evaluating the electrochemical characteristics of MH electrodes.