Study of formation of LiCoO2 using a modified Pechini aqueous sol–gel process

Abstract

In the present study the formation of lithium cobaltite using a modified Pechini aqueous sol–gel process was investigated. The gelling processes in the lithium–cobalt–citric acid system in 1.1:1:1 molar ratio was performed at 80 °C using aqueous solutions of 0.25 mol/dm3 of Co(NO3)2·6H2O with Li(NO3)·6H2O or Co(CH3COO)2·6H2O with Li(CH3COO)·2H2O, respectively. The study of the mechanism of gelling of transition metal ion Co(II) in aqueous medium in the presence of lithium ions and citric acid as chelating agents was approached using mainly UV–Vis and FTIR spectroscopic methods. The UV–Vis spectroscopy indicated that the Co(II) ions are in a tetragonal distorted geometry characteristic to a D4h group symmetry in the solutions in the early steps of the gels formation. After gelling at 80 °C it was observed that the symmetry of the Co(II) ions becomes octahedral (Oh). From the FTIR spectra based on the frequency separation between the antisymmetric stretching νas(COO−) and symmetric stretching νsym(COO−) vibrations, it was identified that the carboxylic groups are bond as a bridging ligands. Using X-ray photoelectron spectroscopy it was identified that the cobalt is present in both final gels as Co(II) ions and the citrate ions are covalently bonded to the cobalt ions. The thermogravimetric/differential thermal analysis showed the thermal stability of the studied gels is higher in the low temperature range for the gels prepared using acetates. Based on the thermal analysis the Li–Co–CA gels were calcinated at 700 °C for 6 h and for each gel a monophasic LiCoO2 was obtained.