Structural Stability of LiCoO₂ at 400°C

Author： Shao-Horn Y. Hackney S.A. Kahaian A.J. Thackeray M.M.

ISSN： 0022-4596

Source： Journal of Solid State Chemistry, Vol.168, Iss.1, 2002-10, pp. : 60-68

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Abstract

The relative stability of the lithiated-spinel structure, Li₂[Co₂]O₄, at 400°C to the layered LiCoO₂ structure has been investigated. “Low-temperature” LT-LiCoO₂ samples were synthesized at 400°C by the solid-state reaction of Li₂CO₃ with CoCO₃ (or Co₃O₄) for various times between 10 min and 232 days. Least-squares refinements of X-ray powder diffraction patterns were used to determine the fractions of lithiated-spinel Li₂[Co₂]O₄ and layered LiCoO₂ in the samples. X-ray powder diffraction and transmission electron microscope data show that Li₂[Co₂]O₄ nucleates from an intermediate Li_xCo_1-x[Co₂]O₄ 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 400°C and support the arguments that a non-ideal cation distribution in Li₂[Co₂]O₄, non-stoichiometry and kinetic factors restrict the transformation of the lithiated-spinel structure to layered LiCoO₂ at this temperature. © 2002 Elsevier Science (USA).