Structural Features of Low-Temperature LiCoO < inf> 2 and Acid-Delithiated Products

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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-LiCoO2samples but that the lithiated-spinel structure was the major phase. Electron diffraction analysis also indicated that some crystallites in the LT-LiCoO2samples had a cation distribution in the spinel notation, {(Li16-4x)16c[Li4x]16d} layer1{(Co16-4x)16d[Co4x] 16c}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-LiCoO2resulted in a lithium-deficient spinel, Li0.8[Co2]O4, with lithium ions on the tetrahedral sites of the spinel structure. The structural features of LT-LiCoO2and the acid-delithiated Li0.4CoO2products provide reasons for the poor electrochemical properties of Li/LT-LiCoO2cells and are consistent with earlier studies. © 1998 Academic Press.

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Journal of Solid State Chemistry