Improved performance of a metal hydride electrode for nickel/metal hydride batteries through copper-coating

Four important properties (exchange current density, apparent activation energy, high-rate dischargeability and discharge potential) were studied for a LaNi4.7Al0.3 metal hydride (MH) electrode fabricated using alloy powders coated with copper. A half-cell set-up was employed with a 6 M KOH electrolyte solution. The results are compared with those for a similar electrode without the Cu-coating. The exchange current density and apparent activation energy for the MH electrode reaction have been evaluated using the potentiodynamic method. The Cu-coated powder electrode showed improved performance, i.e., a higher exchange current density, larger high-rate dischargeability and lower discharge potential, compared to the electrode made with uncoated alloy powder. Thus, Cu-coating ensures both stable discharge performance and high specific power of a Ni/MH battery. This improvement may be due to the following two reasons: (i) corrosion or oxidation protection of alloy powders; (ii) decrease in contact resistance. There is no significant difference between the two apparent activation energies for the electrode reactions for the electrodes with and without the Cu-coating at the same hydrogen concentration.