Preparation And Electrochemical Properties Of Spherical TiO₂ And Li₄Ti₅O₁₂

In the past few decades, considerable attention has been focused on the development of power sources for hybrid electric vehicles (HEVs) and renewable energy systems because of the increasing price of crude oil and global warming crisis. Currently, lithium-ion batteries with high energy density and power density among the rechargeable batteries are regarded as the most suitable application in energy storage device. Electrode materials play a decisive role in the performance of lithium-ion batteries. Spinel and zero-strain Li4Ti5O12 has become one of the ideal anode materials for lithium-ion batteries due to its stable charge and discharge platform,long cycle life,high thermal stability, satisfactory safety,etc. However,poor rate performance caused by its poor conductivity restrict its wide application.In this thesis, the enhanced performance of Li4Ti5O12 is realized by the preparation of high activity of TiO2 precursor and carbon coating. X-ray diffraction (XRD),energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM) are performed to characterize the morphology and structure. The lithium-ion half-cell is assembled by using TiO2 and Li4Ti5O12 as working electrode and lithium metal sheets as counter electrode.Cyclic voltammetry, electrochemical impedance spectroscopy and constant current charge-discharge testing methods are employed to detect the electrochemical performance of the materials.Spherical TiO2 is successfully synthesized by hydrothermal method. The influences of the additive amount of NH4Cl, temperature and synthesis time on the performance of TiO2 are investigated. The results reveal that the optimum condition is the molar amount of NH4Cl 3 times than that of raw material at 120? for 24 hours. The anatase TiO2 synthesized under the optimal condition exhibits charge specific capacitance of 204.1 mAh·g-1 and discharge specific capacitance of 209 mAh·g-1 at 0.1 C, which are higher than those of commercial anatase TiO2 (169.7 and 160.6 mAh·g-1), respectively.Li4Ti5O12 and Li4Ti5O12/C with different coating amounts of carbon original from glucose are synthesized by high temperature solid-state method and the electrochemical properties of the prepared materials are studied. The results show that carbon coated composites exhibit higher electrochemical performance than uncoated and commercial pure phase Li4Ti5O12. The Li4Ti5O12/C composites with the carbon-coated amount of 5.7%present excellent electrochemical performance. The discharge specific capacitance is 172.3 mAh·g-1 at 0.1 C and 123.5 mAh·g-1 at 5 C. The capacity retention after 100 cycles at 1 C and 5 C are 99% and 93.6%, respectively.