Investigation of changes in morphology and elemental distribution in metal hydride alloys after electrochemical cycling

Changes in morphology and elemental distributions in a metal hydride alloy particle after electrochemical charge–discharge cycling were studied using scanning electron microscopy and energy dispersive X-ray analysis. Electrochemical performance evaluation of the metal hydride electrodes included capacity degradation, charge–discharge rate capability, and electrode impedance after a varying number of cycles. These were correlated with the morphology and the elemental distribution changes. Results showed that Al migrates toward the surface from the bulk of an alloy particle as the electrode is cycled. At the same time, the electrode impedance due to charge transfer resistance is reduced significantly. The reduction in impedance correlates with an improved rate capability of the electrode on cycling. The presence of Al in the alloys studied appears to improve cycle life.