Structural features of low-temperature LiCoO2 and acid-delithiated products

X-ray diffraction and transmission electron microscopy were used to study the structural features of low-temperature LiCoO2, (LT-LiCoO2) samples prepared at 400 degrees 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 Li, [Co-2]O-4 (Fd3m) and a layered-type structure (R (3) over bar m) were present in LT-LiCoO2, samples hut 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, {(Li16-4x)(16c)[Li-4x](16d)}(layer1) {(Co16-4x)(16d)[Co-4x](16c)}(layer2)O-32 (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[Co-2]O-4, with lithium ions on the tetrahedral sites of the spinel structure. The structural features of LT-LiCoO2, and the acid-delithiated Li0.4CoO2 products provide reasons for the poor electrochemical properties of Li/LT-LiCoO2, cells and are consistent with earlier studies. (C) 1998 Academic Press.