The effect of ZnO addition on the electrochemical properties of the LaNi3.55Mn0.4Al0.3Co0.2Fe0.55 electrode used in nickel-metal hydride batteries

The studied electrochemical properties of the LaNi3.55Mn0.4Al0.3Co0.2Fe0.55 alloy showed a rather poor performance. To improve them, ZnO, a doping agent at different small amounts (0, 1, or 2.5 wt%), was added to this base alloy. Then, the prepared electrodes were investigated by various electrochemical techniques. The maximum discharge capacity, obtained after the activation procedure, increased with the rise in ZnO content. The activation, as well as the reversibility of the hydrogen absorption/desorption process, were significantly improved with the addition of ZnO. It was observed that the latter did not affect considerably the stability and the cycling lifetime if added to the electrodes. After 30 charge/discharge cycles, the diffusion coefficients were estimated to be 1.55 x 10(-11), 1.30 x 10(-11), and 6.05 x 10(-11) cm(2) s(-1), respectively, for ZnO containing 0, 1, and 2.5 wt%. The ZnO catalyzed the kinetics of hydrogen absorption and desorption process thanks to capacity change before and after activation.