Effects of nickel coating on the properties of metal hydride electrodes

(LM)Ni4.49Co0.1Mn0.205Al0.205 hydrogen storage alloy powder was coated with 25 wt.% Cu by electroless plating in an acidic bath, compacted into disk-type electrodes at room temperature and the disks were finally coated with nickel by electroplating or sputtering. The characteristics of the metal hydride electrodes were examined through electrochemical measurements, scanning electron microscopy and mechanical testing. The nickel coating, when its amount was less than 2.5 wt.%, has improved the properties of electrodes, especially the cycle life and mechanical endurance. The effects were more significant when the nickel coating was done after one charge-discharge cycle or by sputtering. The mechanical strength of the electrodes increased on nickel coating but was not sufficient to prevent the alloy powder from falling off from electrode during cycling in the open half-cell.