The structure and microstructure changes of electrode active materials, β-Ni(OH)2 and AB5 alloy, during the charge and discharge processes have been studied detailed by means of X-ray diffraction (XRD). Physical behavior of electrode active materials and the physical conductive mechanism have been discussed. It has been found that the phase transformation from β-Ni(OH)2 to β-NiOOH do not be observed during the charge process. Until full charge or over charge, partial β-Ni(OH)2 is transformed into γ-NiOOH and both the phases β-Ni(OH)2 and γ-NiOOH always co-existed. During the process of charge, H＋ is not offered by the phase transformation from β-Ni(OH)2 to β-NiOOH, but by the hydrogen atom disengaging from lattice position of β-Ni(OH)2. In the side of negative electrode, solid solution of AB5-H is formed by hydrogen atom inserting into interstitial positions of the AB5 lattice. AB5Hx is formed only when volume change of AB5 reached certain percent. These processes make microstructure of the electrode active materials to occur change and such changes are not fully reversible. To be brief, the physical conductive mechanism of MH/Ni batteries is the directional migrating and moving of hydrogen ions between the positive and negative electrodes because hydrogen atoms are inserting into and deviating from the β-Ni(OH)2 and AB5.

Key words: MH/Ni battery, electrode active material, microstructure, conductive mechanism, X-ray diffraction (XRD)