Structure And Properties Analysis Of Lithium Titanate Synthesized By Hydrothermal Method As Anode Materials For Lithium-ion Batteries

In resent years, lithium titanate has become one of the most attractive anode materials for lithium-ion batteries owing to the zero-strain effect, stable charge and discharge platform, and excellent cycle stability. But the disadvantage of lithium titannate,such as the low electronic conductivity and low specific capacity,which go against its wholesale applications. It has been reported that different morphologies are expected to play an important role in lithium intercalating activity and cycling stability of electrode materials. Therefore, proper morphology, structure and particle size are necessary for Li4Ti5O12 to be employed as an anode material for lithium ion batteries.In this paper, the mesoporous lithium titanate microspheres and lithium titanate nanowires were respectively synthesized by hydrothermal method. Then the optimal synthetic conditions were discussed and obtained. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy(TEM), specific surface area analysis and Laser particle sizer analysis. Moreover, the charge and discharge capacity and cycle performance of the samples were studied by galvanostatic charge and discharge tests. Then formation processes of lithium titannate mesoporous microspheres and nanowires were preliminary proposed.The mesoporous microspheres of lithium titanate with spinel structure were synthesized with tetrabutyl titanate, ethanol, lithium hydroxide as raw materials. The effects of amount of lithium hydroxide, hydrothermal time and sintering temperature on properties of sample were studied. Then, the synthesis mechanism was briefly studied.The results indicated that when 2.55mmol LiOH·H2O reacted with 0.2g hydrolysate, the sample had pure phase.When the hydrothermal condition was 36h and 180℃,the structure of sample particle was perfectly spherical.The average volume size of samples was between 400nm and 600nm.The charge and discharge voltage plateau of samples was very stable. When the sintering temperature was 700℃, the first discharge capacity was 148.3mAh/g at 0.1C.After 10th cycle,the discharge capacity retained at 132.5mAh/g. The ratio of capacity retention was 89.3%. The BET pecific surface area of Li4Ti5O12 microspheres was 17.19m2/g. The BJH pore volume and average pore diameter was 0.037cm3/g and 1.68nm, separately. The content of mesoporous pore was about 92%. The possible formation process is that tetrabutyl titanate hydrolyzes to the hydrous TiO2 microspheres in the existence of KCl, firstly. During the reaction in hydrothermal method, lithium ions exchange with the cation in the hydrous TiO2 microspheres. After that, the complex Li-Ti-O-H system has formed. Finally, aftering sintering, the mesoporous spheres of Li4Ti5O12 has obtained.The nanowires of lithium titanate were synthesized with TiO2 powders, sodium hydroxide, hydrochloric acid and lithium hydroxide as raw materials. The effects of hydrothermal temperatures and hydrothermal time on the morphology of titanic acid were studied. The effects of concentration of LiOH and sintering temperatures on the properties of lithium titanate nanowires were also analysed. Then the synthesis mechanism of Li4Ti5O12 nanowires was preliminary analyzed. The results indicated that When the hydrothermal condition was 180℃and 48h, the morphology of titanic acid was the best. The diameter of nanowires was about 80-200nm, and the length of nanowires was about 6-8μm. When the concentration of LiOH was 0.2mol/L and the sintering temperature was about 500-600℃, the diameter of Li4Ti5O12 nanowires is about 100-300nm and the length is about 3-5μm. The grain sizes of samples decreased with the increase of sintering temperatures. When the sintering temperature was 500℃, the first discharge capacity of lithium titanate nanowires was 143.4mAh/g at 0.1C.And the first discharge capacity was 141.4mAh/g. The BET pecific surface area and BJH pore volume were 13.864m2/g and 0.039cm3/g, respectively. The possible formation process of nanowires is that the TiO2 powders react with NaOH to form sodium titanate nanowires during the hydrothermal process. The titanic acid nawires form after the ion exchange in infusion in HCl. Finally the lithium titanate nanowires form after the hydrothermal process and sintering.