Structural aspects on the charged positive Ni electrode

Abstract

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 β-structure is proposed; hexagonal crystal system with a=2.98(1) and c=4.69(7) Å. We propose a structural model of the charged phase as consisting of disordered separate domains in the ab-plane. The conventional γ-phase is proposed to constitute of a modification of the β-NiOOH structure and is usually supposed to contain vacancies/defects in the c-direction. We show in this paper that the γ-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) Å, respectively.