Journal of Power Sources, Vol.107, No.1, 34-41, 2002
Structural aspects on the charged positive Ni electrode
X-ray powder diffraction (XPD) and neutron powder diffraction (NPD) measurements in combination with theoretical calculations were performed on discharged and charged positive material of the Ni hydroxide electrode. The Ni(OH)(2) in the battery material is disordered to a large extent and show large contributions of amorphous phases. The results of this investigation indicate similar local structures for the discharged and the charged phases. During charging, the c-direction remains essentially unaffected, whereas the ab-plane shows a high degree of disorder resulting in the disappearance of the [1 0 0] peak. A NPD pattern was used for indexing and refining of unit cell parameters. A revised conventional unit cell for the charged beta-structure is proposed; hexagonal crystal system with a = 2.98(1) and e = 4.69(7) Angstrom. We propose a structural model of the charged phase as consisting of disordered separate domains in the ab-plane. The conventional gamma-phase is proposed to constitute of a modification of the beta-NiOOH structure and is usually supposed to contain vacancies/defects in the c-direction. We show in this paper that the gamma-phase may also be interpreted as consisting of partial systematic defects in the ab-plane. This phase can be indexed with an orthorhombic cell: a = 7.50(2), b = 4.83(2) and c = 3.97(1) Angstrom, -respectively.