Sol-gel Preparation Of Licoo <sub> 2 </ Sub> Of Lico <sub> 0.8 </ Sub> Ni <sub> 0.2 </ Sub> O <sub> 2 </ Sub> Thin Film Materials

Rcently, more and more electronic devices come forth, with smaller dimension, all solid state thin films and less weight. Micro-electronic mechanical system (MEMS) also develops rapidly. They all need micro-batteries to match with. All-solid-state thin film lithum micro battery will become the most popular type of the recharge micro-battery in the future, because of its high capacity, stable working voltage, superior energy density, low-self-discharge rate, and long cycle life. Thin flim cathode, as an important part of all-solid-state thin film lithum micro battery has been therefore the focus of the research. Researchers all over the world are applying themselves to improve its capability, reduce its cost, and reform its fabrication method. Based on this, we chose potential LiCoO₂ and Ni-doping LiCo_0.8Ni_0.2O₂ thins films as cathode materials and used sol-gel method to do the research. In this paper, the fabrication processes of LiCoO₂ and Ni-doping LiCo_0.8Ni_0.2O₂ thins films had been investigated. The effect on microstructure and properties of LiCoO₂ and Ni-doping LiCo_0.8Ni_0.2O₂ thins films caused by fabrication processes had also been discussed.Two raw materials lithium acetate and cobalt acetate were mixed and dissolved in glycol together with litric acid as a chelating agent. Lithium acetate and cobalt acetate were used to replace lithium acetylacetonate and cobalt acetylacetonate because of their low prices. The coating solution was stable,viscid,and transparent dark-purple in color, which was obtained by a new method without distillation. The LiCoO₂ films were fabricated on Si(100) substrates,Si(111)substrates,Pt(111)/Ti/SiO2/Si substrates and stainless steel substrates by the spin-coating method respectively. The factors of affecting the quality of thin films were also discussed, including the concentration of the solution, the quantity of citric acid, rotational speed and time, the rate of increasing temperature, and the evaporating temperature and time.X-ray diffraction analysis was performed to identify the crystalline phase of the final films. The morphology and surface roughness of the final film were studied with scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. X-ray photoelectron spectroscopy (XPS) was used to measure the elements in the films. The electrochemical properties of the LiCoO₂ cathode thin films fabricated on stainless steel substrates were investigated in a test cell consisting of a thin film cathode, 1M LiPF6/EC+DEC+DMC(1:1:1) liquid electrolyte, and an anode of lithium foil. It was found that the electrochemical properties of the thin film varied markly as the annealing temperature and time changed.The best electrochemical behaviour was obtained from a film annealed at 700°C for 30 minutes, which had the largest initial discharge capacity (38μAh/(cm2·μm)) and moderate rechargeability (capacity retention was 90.2% after 20 cycles.).The LiCo_0.8Ni_0.2O₂ films had also been fabricated on Pt (111)/Ti/SiO2/Si substrates and stainless steel substrates respectively by a sol-gel method using a spin coater and Ni-doping. The crystalline phase and the morphology of the final films were studied with X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM), respectively. X-ray photoelectron spectroscopy (XPS) was used to measure the elements in the films. Compared with the LiCoO₂ thin films annealed at the same conditions, the electrochemical properties of the LiCo_0.8Ni_0.2O₂ thin films deposited on stainless steel substrates and annealed at 700°C for 30 minutes, had larger initial discharge capacity (39.7μAh/(cm2·μm)).