Factors Influencing the Layered to Spinel-like Phase Transition in Layered Oxide Cathodes

Co, Ni, and compositions obtained by chemically extracting lithium with from have been investigated by X-ray diffraction after heating at various temperatures. While obtained from both the monoclinic (O3 stacked layer structure) and orthorhombic transforms to the spinel-like phases at ambient temperature during the lithium extraction process due to cation migration, needs mild heat (∼150°C) to transform to the spinel-like phase. does not transform even after heating at 200°C. The decrease in the structural stability in the order is explained on the basis of crystal field stabilization energies. Additionally, the incorporation of foreign cations into the transition metal planes via cationic substitutions is found to increase the structural stability by perturbing the cooperativity among the transition metal ions and thereby suppressing the cation migration. © 2002 The Electrochemical Society. All rights reserved.