Effect of surface modification on the performance of negative electrodes in Ni/MH batteries

Abstract

The performance of a Nickel/Metal Hydride (Ni/MH) battery closely depends on the characteristics of the negative MH electrode. Exchange current density, high-rate dischargeability, discharge potential and apparent activation energy of a MH electrode are very important properties, among which the high-rate dischargeability and discharge potential of a MH electrode determine the specific energy and specific power of electric vehicles (EVs) when Ni/MH batteries are applied to EVs. Significant improvements in exchange current density, high-rate dischargeability and discharge potential of a MH electrode have been observed for a 9.0 wt % copper coated LaNi 4.7Al 0.3 MH electrode. The high-rate dischargeabilities were determined to be 88.4% for the LaNi 4.7Al 0.3 electrode and 99.4% for Cu-coated LaNi 4.7Al 0.3 electrode. The discharge potential for the Cu-coated LaNi 4.7Al 0.3 electrode is lower (i.e. more negative) than that for the LaNi 4.7Al 0.3 electrode, especially at a large discharge current density (i.e. 200 mA g −1 ). The discharge potentials of the Cu-coated LaNi 4.7Al 0.3 electrode are almost the same value (i.e. −0.930 V vs. Hg/Hgo) at both 20 and 200 mA g −1 discharge current densities. There is no significant difference between the two apparent activation energies for the electrode reactions for the electrodes with and without the microencapsulation of the MH powders at the same hydrogen concentration.