Structural stability of LiCoO2 at 400°C

The relative stability of the lithiated-spinel structure, Li-2[Co-2]O-4, at 400degreesC to the layered LiCoO2 structure has been investigated. Low-temperature LT-LiCoO2 samples were synthesized at 400degreesC by the solid-state reaction of Li2CO3 with CoCO3 (or Co3O4) for various times between 10min and 232 days. Least-squares refinements of X-ray powder diffraction patterns were used to determine the fractions of lithiated-spinel Li-2[Co-2]O-4 and layered LiCoO2 in the samples. X-ray powder diffraction and transmission electron microscope data show that Li-2[Co-2]O-4 nucleates from an intermediate LixCo1-x[Co-2]O-4 spinel product before transforming very slowly to layered LiCoO2. The experimental data confirm the theoretical prediction that layered LiCoO2 is thermodynamically more stable than the lithiated-spinel structure at 400degreesC and support the arguments that a non-ideal cation distribution in Li-2[Co-2]O-4, non-stoichiometry and kinetic factors restrict the transformation of the lithiated-spinel structure to layered LiCoO2 at this temperature. (C) 2002 Elsevier Science (USA).