Fabrication, Structure And Electrochemical Properties Of TiO₂Anode Materials For Lithium Ion Batteries

Anatase TiO2possesses a much higher operating voltage (～1.7V vs. Li/Li+) than traditional carbon-based anode materials, avoiding the formation of the solid electrolyte interphase (SEI) and increasing safety, especially at high rates and elevated temperatures. Furthermore, TiO2is abundant and cheap, and shows low self-discharge, good cyclabilty and excellent high-rate retention. In summary, anatase TiO2demonstrates broad application prospects as a new type of lithium-ion anode materials. However, the performance of TiO2anode materials is limited by its poor conductivity, so improving the electric conductivity and diffusivity of Li-ions is the key to realize its further applications. Pressurized calcination method and solvothermal method are introduced in this thesis to prepare TiO2and TiO2/C composites using titanium ethoxide (C8H20O4Ti) as precursor. The effects of synthesis conditions including the different carbon source, surfactants, reaction temperature and conductive agent on the structure and electrochemical properties of TiO2and TiO2/C composites are investigated by X-ray diffraction, scanning electron microscope, element analysis and electrochemical testing of galvanostatic charge-discharge, cyclic voltammetry, electrochemical impedance spectra etc.The results show that the TiO2nanoparticles produced by pressurized calcination method aggregate to form large second-particles with diameters of2-5μm, and result in severe capacity decay. Different carbon sources have been introduced to prepare TiO2/C composites. Compared with other carbon sources, VGCF results in most excellent cycling performance and high rate capability due to the3D network morphology, which not only assists the electron transfer but also facilitates lithium ion diffusion.Compared with other surfactants, TiO2synthesized by a solvothermal method using PVP K-30as surfactant have relatively narrow particle size distribution and deliver better electrochemical properties. Different reaction temperature strongly affects the morphology and electrochemical properties of TiO2. The experimental results show that TiO2synthesized at150℃exhibits superior discharge capacity of198mAh/g after80cycles and cycling stability due to its small particle size. Finally, modification of TiO2has been carried out using VGCF as conductive agent and using surfactant PVP K-30. The TiO/C composites are fabricated in situ by a solvothermal method. The TiO2/C composites by using PVP K-30as surfactant maintain3D network morphology, resulting in significant improvement of discharge capacity of180mAh/g after52cycles and cycling stability.