[Study on the structure of LiCoO2 synthesized by sol-gel with citric acid]

Lithium cobalt oxide was synthesized by sol-gel with citric acid. The crystallization process of LiCoO2 gel precursor was studied by TG-DSC, and then it was calcined from 400 to 800 degrees C. The crystal structures of LiCoO2 powders formed at different temperatures were analyzed through X-ray diffraction, Infrared spectrum, Raman spectrum and transmission electron microscope. The results show that the mean grain sizes of LiCoO2 powders are about 20-40 nm, and increase with calcinating temperature changing from 400 to 700 degrees C, while decrease at 800 degrees C. The structure changed from modified spinel to layered-rock-salt with the calcinating temperature from 400 to 800 degrees C. In the modified spinel structure, Co2+ ions reside at the tetrahedral sites and Co3+ ions reside at the octahedral sites. However, in the layered-rock-salt structure, just only Co3+ ions reside at the octahedral sites.