University of Twente Student Theses
TiNbO nanosheets as a high-rate electrode material for lithium-ion battery
Tang, Jinyao (2021) TiNbO nanosheets as a high-rate electrode material for lithium-ion battery.
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| Abstract: | Lithium-ion batteries have been widely used in mobile electronic equipment, electrical vehicles, and smart energy storage terminals because of their high energy density and good cycle stability. The anode material is an important factor in the performance of lithium ion batteries. However, as the above-mentioned equipment further increases the requirements for the endurance and charging time of lithium-ion batteries, the current commercial graphite-based carbon anode materials can no longer meet the demand. Titanium niobate oxides (TNO) has a high theoretical specific capacity, and the unit cell volume changes little during the deintercalation process of lithium ions so that the reversibility is high. Therefore, it is a new type of high-performance anode material with considerable application prospects. However, its inherently low ionic and electronic conductivity limits the improvements of its electrochemical performance. In this thesis, the TNO (TiNbO5 and Ti5NbO14) was exfoliated into nanosheets and compared with HTNO bulks. First, the exfoliation process of TiNbO5 nanosheets was optimized by comparing the capacity performance of the nanosheets fabricated by previous procedure and the optimized one. The rate charge-discharge test results shows the optimized nanosheets had over 50 mAh/g at 20C, which is higher than the older one. The optimized method is to dry the protonated powder at room temperature overnight and neutralize the exfoliation solution with acid. The nanosheets are obtained by being washed and dried at room temperature in a vacuum oven. Second, the exfoliation condition of Ti5NbO14 nanosheets was explored. The nanosheets exfoliated at different conditions were deposited on a Si substrate by Langmuir-Blodgett deposition and characterized by Atomic force microscopy. The most efficient exfoliation condition is to mix 0.4g H3Ti5NbO14, 2.11 mL TBAOH and 80 mL deionized water to react for 24 hours. After that, the TiNbO5 nanosheets, Ti5NbO14 nanosheets, HTiNbO5 bulk and H3Ti5NbO14 bulk were characterized by X-ray diffraction and Scanning electron microscopy to analyze the crystal lattice and morphology of the research objectives. It can be seen the nanosheets samples have fluffy layered structures which lead to a larger inner area. Finally, the electrochemical characterization was carried on the four active materials for rate charge-discharge test, cyclic voltammetry, electrochemical impedance spectroscopy and long cycling test. The results show the HTiNbO5 bulk had best performance among the four materials with highest lithium ion diffusion coefficient and contribution of pseudocapacitance. The nanosheets with Ti : Nb ratio of 1 : 1 perform better than nanosheets with 5 : 1 ratio, while same results show in bulk samples. The reason is that Nb5+/Nb4+ redox reaction is controlled reaction in the whole process, and the samples with higher Nb percentage have better lithium ion diffusion ability with a result of higher specific capacity. The nanosheets samples are not good as expected due to their fluffy layered structure and their inner area cannot be coated with the carbon black so that the conductivity is affected and the capacity is lower than expected. Key words: Lithium ion batteries, Anode materials, TiNbO5 nanosheets, Ti5NbO14 nanosheets, HTiNbO5 bulk, H3Ti5NbO14 bulk, Exfoliation. |
| Item Type: | Essay (Master) |
| Faculty: | TNW: Science and Technology |
| Programme: | Chemical Engineering MSc (60437) |
| Link to this item: | https://purl.utwente.nl/essays/103516 |
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