Preparation And Electrochemical Properties Of Nano-NiO By Sol-gel Method

The dielectrical property, electrochromic and catalytic performance of NiO as a typical transition-metal oxide has been sufficient examined. However, there are few reports on its great advantages as one of new and efficient anode materials of thin film lithium ion battery for high specific capacity. Sol-gel method has some advantages such as simple equipments required, excellent stoichiometric ratio, low cost and high deposited rate, hence it is quite promising and facile rout for industrial applications. In this paper, the sol and gel were synthesized with the nickel diacetate as the nickel source, PAA as the chelator and the deionized water as the solvent, respectively. The NiO thin film was deposited on the stainless and single crystal silicon substrate via spin-coating technique combined with heating treatment process, and the NiO powder was prepared by some heat treatment techniques. The influence of sol viscosity, drying condition, heating rate and sintering treatment parameter on morphology and structure of NiO film were examined. The thermal decomposition behavior of gel precursor and the structure, morphology and electrochemical properties of NiO thin film and NiO powder were characterized by thermogravimetric/differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) and the constant current charge/discharge technology. In addition, the reaction mechanism between NiO and Li was investigated by the electrochemical impedance spectroscopy. The detailed results in this dissertation include:1. The stable sol is prepared with nickel diacetate as the nickel source, PAA as the chelator and deionized water as the solvent via macromolecule complex at some temperature. The gel completely decomposes at 450℃and gradually forms the nanocrystalline NiO and its size becomes larger with the increasing of sintering temperature.2. Results show that the organic matter is easy to volatilize by increasing the drying temperature, decreasing the viscosity of sol and reduceing the heating rate.A smooth, uniform, compact and free of cracks NiO thin film has prepared if the viscosity of sol is 5.45cst, the dying temperature is 200℃and the heating rate is 0.5℃/min.3. The crystal structure of NiO thin film becomes integrity and the size of paticles become larger with the increasing of sintering temperature. The NiO thin film sintering at 500℃for 2h exhibits high discharge specific capacity and well cycle performance whose initial and stable discharge specific capacity after 100 cycles are 1147.5mAh/g and 500mAh/g respectively with a capacity loss of 1% per cycle at the current density of 0.01mA/cm². These electrochemical performances will be bad if the current density increases.4. The proposed equivalent circuit of R_S(Q_dl(R_CtZ_W))(Q_SEIR_SEI) can reasonably explain the process of reaction between Li and NiO electrode and preferable simulate the EIS measurement data with all the errors lower than 10%. The SEI film grows slowly with polarizing voltage reducing and completely forms at 0.6V in the 1st discharge. The Li pass through SEI film to react further with NiO, then grains Ni and amorphous Li2O matrix obtained. In the charge course the SEI film partially decomposes and Li and NiO formed by reversible reaction of Li2O and Ni.5. The nano-NiO powder is prepared by heat treatment of xerogel. The size of nanocrystalline NiO becomes larger with the increasing of sintering temperature and the extending of time. The NiO powder sintered at 600℃for 8h possesses the initial discharge specific capacity about 800mAh/g and remains 500mAh/g after 20 cycles at the cut-off voltage of 0-3V and the current density of 0.1mA/cm². Further more, it can stand quick charge and discharge with high current density of 0.2mA/cm² and has fine cycling performance.