Dispersion Technology and Its Applications to the Fabrication of Nano-ceramics and Electrode of Lithium Ion Battery
2007
Hochschulschrift
Zugriff:
96
This thesis discusses the dispersion technology and their applications to the fabrication of barium titanate (BaTiO3, BTO)-relating nano-ceramics and LiCoO2 electrode of lithium ion battery (LIB). The BTO-relating ceramics include the genuine BTO, Ba0.7Sr0.3TiO3 (BST) and La2O3-doped BST (LBST). An amphibious dispersant, polyacrylamide/(��-N, N-dimethyl-N-acryloyloxyethyl) ammonium ethanate (PDAAE), and an anionic dispersant, poly(methacrylic acid) (PMAA-Na), were adopted to the dispersion of nano-ceramics. A new dispersant, poly(4-{4-[di(4-aminophenyl)methyl]phenoxy}phthalic ether imide) (PEI), was synthesized for the dispersion of carbon nanotube (CNT) conduction agent in LiCoO2 electrode so as to improve the performance of high power LIBs. BST-relating nano-ceramic powders were prepared via a physical grinding in conjunction with the chemical dispersion. Dispersion properties including viscosity, sedimentation volume, particle size distribution, zeta-potential and isothermal adsorption were investigated so as to determine the optimal dispersion condition. The capacitor samples were then prepared by appropriate sintering process and then dielectric property measurement was followed. It was found that specific control on sintering condition is required for the nano-ceramic powders to achieve desired microstructure, crystalline phase and dielectric properties of devices. The major achievements in BTO-relating nano-ceramics are as follows. BTO sample sintered at 1100�aC for 6 hrs possesses relatively small grain sizes (about 140 nm), high density (about 95% T.D.) and distinct room-temperature dielectric properties (dielectric constant = 8000; dielectric loss = 5×10�{3). High-density (�d 95%) BST samples with desired dielectric properties could be obtained via sintering at 1200�aC for 6 hrs (grain size �l 200 nm; dielectric constant = 9700; dielectric loss = 0.04) or at 1300�aC for 1 hr (grain size �l 220 nm; dielectric constant = 9800; dielectric loss = 0.075). Besides, the BST samples exhibited a lower Curie point (TC) in comparison with conventional BTO and BST systems. The 1.0 mol.% La-doped BST sample sintered at 1400�aC for 1 hr possesses the finest grain size about 200 nm, the highest dielectric constant about 13800 and lowest dielectric loss about 2.8×10�{4. In the part relating to the dispersion of CNT, the optimal amount of PEI (about 2 wt.% relating to the weight of CNT) was determined by means of the studies of adsorption isotherm, rheology and sedimentation behaviors. Electrochemical impedance spectroscopy (EIS) revealed that the ac resistance of electrode decreases from 287 �� for cell without PEI to 161�� for the cell at containing optimal amount of PEI. This is attributed to the network established by dispersed CNTs that effectively promotes the charge carrier migration in electrode. The C-rate test indicated that at the high-rate discharge test results, that the LIB test cell with modified electrode possesses 8 C-discharge capacity of 101 mAh/g, which is about 74% of its 0.2 C-discharge capacity. The results of high rate capability and long cycle life evidences the promising applications of such a LIB to power sources, e.g., power tools, electric bicycle, electric motorcycle, etc.
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Dispersion Technology and Its Applications to the Fabrication of Nano-ceramics and Electrode of Lithium Ion Battery
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Autor/in / Beteiligte Person: | 應國良 |
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Veröffentlichung: | 2007 |
Medientyp: | Hochschulschrift |
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