Structural Features of Low-Temperature LiCoO₂ and Acid-Delithiated Products

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

ISSN： 0022-4596

Source： Journal of Solid State Chemistry, Vol.140, Iss.1, 1998-10, pp. : 116-127

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Abstract

X-ray diffraction and transmission electron microscopy were used to study the structural features of low-temperature LiCoO₂ (LT-LiCoO₂) samples prepared at 400°C either by a simple solid-state reaction or via a sol–gel process. Single-crystal electron diffraction analysis showed that both a lithiated-spinel Li₂ [Co₂]O₄ (Fd3m) and a layered-type structure (R3m) were present in LT-LiCoO₂ samples but that the lithiated-spinel structure was the major phase. Electron diffraction analysis also indicated that some crystallites in the LT-LiCoO₂ samples had a cation distribution in the spinel notation, {(Li_16-4x)_16c[Li_4x]_{16 d}}_layer1 {(Co_16-4x)_16d[Co_4x]_{16 c}}_layer2O₃₂ (0<x<1) that was intermediate between the ideal layered (x=1) and ideal lithiated-spinel (x=0) structures. Electron diffraction confirmed that acid-delithiation of LT-LiCoO₂ resulted in a lithium-deficient spinel, Li_0.8[Co₂]O₄, with lithium ions on the tetrahedral sites of the spinel structure. The structural features of LT-LiCoO₂ and the acid-delithiated Li_0.4CoO₂ products provide reasons for the poor electrochemical properties of Li/LT-LiCoO₂ cells and are consistent with earlier studies.