Vapor Growth and Chemical Delithiation of Stoichiometric LiCoO2 Crystals

Single crystals of LiCoO2 have been grown by a vapor transport method at high temperature and normal atmospheric pressure. The plate-like single crystals have large (00l) facets (up to 1 mm2) and thicknesses ranging from 5 to 50 μm. A single-crystal X-ray diffraction study confirmed the trigonal R3̅m space group with lattice parameters a = 2.8150(3) Å and c = 14.0516(6) Å at room temperature. Electrical transport measurements indicated that as-grown crystals are highly insulating, with electrical resistivity in the order of TΩ cm at room temperature. This contrasts with the value of 5 Ω cm previously reported for a flux-grown crystal and suggests that vapor growth crystals may have fewer defects. Li-ion deintercalation of LiCoO2 crystals was carried out by a chemical extraction process. A quasi-in situ XRD approach was utilized to monitor the structural evolution during the Li-ion extraction process, which exhibited the progression of phases widely established for this system, but also shows evidence of inhomogeneous delithiation mechanism. Transport measurements confirm metallic behavior for delithiated LixCoO2 crystals (0.5 x < 1.0) with anomalies in the temperature of 150–180 K.