C. Delmas, C. Faure, Y. Borthomieu
Mar 30, 1992
Citations
2
Influential Citations
46
Citations
Journal
Materials Science and Engineering B-advanced Functional Solid-state Materials
Abstract
Abstract New hydrated cobalt-substituted nickel hydroxides were prepared and characterized. These materials were obtained either by precipitation (α) or by the “chimie douce” technique ( α ∗ and α′). Cobalt generally stays in the trivalent state. In contrast with the α Co 2+ phases, the α Co 3+ phases are stable in KOH if at least 20% cobalt is substituted for nickel to compensate for the excess of positive charge resulting from the presence of trivalent ions in the brucite-type layers, anions (sulphate or carbonate) are inserted between the Ni1−xCox(OH)2 slabs. In the case of well-crystallized α ∗ phases, an interstratified packing is obtained for low cobalt contents ( x ). As shown by a study of the physical properties, the electronic conductivity of the oxidized phases ( γ Co )increases with the amount of cobalt. These phases were used as the positive electrode material of Ni/Cd cells. At the beginning of cycling, 1.33− per (Ni + Co) atom can be reversibly exchanged between the γ and α phases. During long-range cycling tests, a slow evolution from the γ/α system to the β(III)/β(II) system is observed. This point is discussed in relation to the amount of cobalt.