Synthesis of LiCoO2 thin films by sol/gel process
Résumé
LiCoO2 thin films were synthesized by sol/gel process using acrylic acid (AA) as chelating agent. The gel formulation was optimized by varying solvent (ethylene glycol or water) and precursors molar ratios (Li, Co, AA) in order to obtain a dense film for positive electrode of lithium batteries. The gel was deposited by spin-coating technique on an Au/TiO2/SiN/SiO2/Si substrate. Thin films were deposited by either single or multistep process to enhance the density of the thin film and then calcined during 5 h at 800 °C to obtain the R-3m phase (HT-LiCoO2). A chemical characterization of the solution was realized by Fourier Transform Infrared (FTIR) spectroscopy. Thermal decomposition of precursors and gel was studied by Thermo Gravimetric Analyses (TGA). Further investigations were done to characterize rheologic behaviour of the gel and solvents affinity with the substrate. Crystallinity and morphology were analyzed respectively by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The formation of R-3m phase was confirmed by the electrochemical behaviour of the gel derived LiCoO2. Cyclic voltammograms and galvanostatic cycling show typical curve shape of the HT-LiCoO2.