Probing lithium and vacancy ordering in O3 layered LixCoO2 (x » 0.5)

X-ray and electron diffraction experiments were performed to understand lithium and vacancy ordering phenomenon and the monoclinic distortion in Li0.5CoO2. It was shown that the observed peak splitting, indicative of monoclinic distortion, was attributed primarily to the shearing of the rhombohedral oxygen lattice. Experimental electron diffraction studies of a monoclinic Li0.5CoO2 sample revealed additional reflections that were consistent with the in-plane ordering configuration of lithium and vacancy proposed previously by Reimers and Dahn [J. Electrochem. Soc., 139, 2091 (1992)]. Moreover, this study found that the electron diffraction patterns with appearances resembling those of the spinel structure could be explained fully by the formation of mazed microstructure and lithium ordering in Li0.5CoO2. Therefore, there was no evidence of the layered to spinel transformation in the LixCoO2 system, in agreement with the excellent cycling performance of Li/LixCoO2 batteries.