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URN etd-0827112-145614 Statistics This thesis had been viewed 1746 times. Download 280 times. Author Chao-chia Hsu Author's Email Address No Public. Department Chemical Engineering Year 2011 Semester 2 Degree Master Type of Document Master's Thesis Language English Page Count 109 Title SYNTHESIS BY SOL-GEL METHODE AND CHARACTERIZATION OF CATION DOPING AND CARBON COATING Li4Ti5O12 ANODE MATERIALS FOR LITHIUM ION BATTERIES Keyword carbon coating anode material Al-doping Lithium titanate Lithium-ion batteries Lithium-ion batteries Lithium titanate Al-doping anode material carbon coating Abstract In this study, the samples of Li4Ti5O12 with or without Al-doping were synthesized by sol-gel method. The crystal structure and surface morphology were characterized by X-ray diffraction and scanning electronic microscopy, while the electrochemical performances including charge/discharge test, cyclic voltammetry, and electrode impedance spectroscopy were also investigated. The results revealed that the discharge capacity of Li4Ti5O12 and Al-doped Li4Ti5O12 at 0.1C were almost the same, which were 168.7 mAh g-1 and 162.6 mAh g-1, respectively. However, a large discrepancy in the discharge capacity between Li4Ti5O12 (73.0 mAh g-1) and Al-doped Li4Ti5O12 (107.4 mAh g-1) can be observed while the C rate was increased to 5 C. The capacities were further improved about 50 mAh/g when the charged and discharged between 0-2.5 V. The discharge capacity of Li4Ti5O12 and Al-doped Li4Ti5O12 at 0.1C were 221 mAh g-1 and 228 mAh g-1, respectively. When increasing the C rate to 5 C, a significant discrepancy in the discharge capacity between Li4Ti5O12 (173.3 mAh g-1) and Al-doped Li4Ti5O12 (190.0 mAh g-1) can be observed. Al3+ doping indeed enhanced the characteristics of lithium diffusion and electronic conductivity in the electrode; as indicated by cyclic voltammetry and AC impedance spectra. As a result, Al3+ doping does not change the electrochemical process, instead enhanced lithium diffusion, electronic conductivity, and high C-rate capability. On the other hand, the charge-transfer resistance and solution resistance also can be decreased.
Additionally, C/Li4Ti5O12 composites were prepared by using graphene and PEDOT. The Li4Ti5O12 mixed with graphene still maintain good electrochemical properties. The Li4Ti5O12 mixed with PEDOT exhibited poor capacity although it still retained good cycle stability.
Advisor Committee Jeng-yu Lin - advisor
Mao-sung Wu - co-chair
Tsung-wu Lin - co-chair
Files Date of Defense 2012-07-06 Date of Submission 2012-08-28