【作者】 李伟；

【导师】 张乃庆；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2010， 硕士

【摘要】 随着能源与环境问题日益突出,电动汽车（EV）和混合动力汽车（HEV）的研究越来越受到世界范围内研究者关注。锂离子电池技术在EV和HEV中应用所面临的主要问题是快速充放电和安全性问题,限制其快速充放电性能的主要原因是锂离子在固相中扩散速率较低。TiO₂材料由于其较高的充放电电压、高化学稳定性、充放电过程“零”应变,且具备开放的嵌脱锂通道等特点,可实现快速充放电及满足安全性要求,成为一种新兴的动力锂离子电池负极材料。采用纳米材料可以有效的缩短锂离子迁移路径,增大电化学活性比表面,从而大幅度提升材料的快速嵌脱锂能力。近年来,离子液体在纳米材料合成中的应用日益增多,并显示出其相比于传统合成方法的突出优势。基于此,本文分别采用离子液体水解合成及溶胶-凝胶法合成TiO₂纳米晶,系统探讨了合成温度、辅助溶剂、阴离子种类、碳链长度等对合成TiO₂晶型及微观形貌的影响,并对合成的TiO₂纳米晶的电化学嵌脱锂性能进行了深入研究。此外,为改善TiO₂的电子和离子导电性,分别对其进行石墨烯（Graphene,GE）复合及氟F掺杂。首先,采用离子液体水解合成TiO₂,在高卤素离子和高酸度的条件下得到了大比表面的金红石TiO₂纳米晶,该材料可逆比容量可达216mAh/g,5C循环200次容量保持在127mAh/g。添加辅助溶剂后,合成产物的晶型发生了转变,得到了锐钛矿TiO₂纳米晶,比表面大大增加,该材料可逆比容量可达192mAh/g,5C循环200次容量保持在119mAh/g。合成中还发现,BF4-可更有效地促进结晶及晶粒的长大,长碳链离子液体表现出了更显著的模板效应。研究发现TiO₂电极的嵌脱锂动力学受锂离子的固相扩散控制。其次,采用离子液体溶胶-凝胶法合成了具有高比表面、孔径分布均匀、高热稳定性的介孔锐钛矿TiO₂纳米晶。同样,长碳链离子液体表现出了更显著的模板剂和稳定剂的作用。该锐钛矿TiO₂可逆比容量可达226mAh/g,5C循环50次容量保持在127mAh/g。最后,采用原位生长的方法制备了金红石TiO₂/Graphene复合纳米材料,采用TiF₄为氟源合成了F掺杂金红石TiO₂,研究发现复合或掺杂后,金红石TiO₂的电化学性能尤其是大倍率充放电能力得到了大幅的提高。更多还原

【Abstract】 Along with the prominent energy and environmental problems, electric vehicle （EV） and hybrid electric vehicle （HEV） are getting more and more attention by researchers worldwide. The main problems for lithium-ion battery technology applied in EV and HEV are the rapid charge-discharge ability and security issues, while the main reason for the restriction of its rapid charge-discharge performance is the low lithium-ion diffusion rate in the solid phase. TiO₂ electrode materials can achieve rapid charge-discharge and meet safety requirements due to their higher charge-discharge voltage, high chemical stability, zero volume strain during the charge-discharge process, and open channel for lithium-ion insertion and extraction. Materials with nano-structure can effectively shorten the lithium-ion deffusion path and increase the specific surface with electrochemical activity, which greatly enhance the material properties of the fast Li-ion insertion and extraction.In recent years, the application of ionic liquids （ILs） in the synthesis of nano-materials has been increasing, which shows excellent advantages compared to the traditional synthetic methods. In view of this, this thesis has studied the function of ionic liquids in the hydrolysis and the sol-gel synthesis of TiO₂ nanocrystals, and the effecting factors such as temperature, auxiliary solvent, anion species and carbon chain length are researched. The electrochemical Li-ion insertion-extraction performance has also been studied. In addition, in order to improve the electronic and ionic conductivity of TiO₂, we have prepared TiO₂/Graphene （GE） composites and F-doping TiO₂.Firstly, we synthesized TiO₂ nanocrystals by hydrolysis using ILs. Rutile nanocrystalline TiO₂ with large specific surface area were fabricated in the high halogen ion and high acidity conditions. This material showed a excellent reversible capacity of 216mAh/g, and the capacity kept 127mAh/g after 200 cycles at 5C. After adding auxiliary solvent, anatase TiO₂ nanocrystals were obtianed, while its specific surface area increased greatly. This material also showed a high reversible capacity of 192mAh/g and maintained 119mAh/g after 200 cycles at 5C. It was also found that BF4-can be more effective in promoting crystallization and grain growth, while Long carbon-chain ionic liquids showed superior template effect. The dynamics of the lithium-ion intercalation-deintercalation of TiO₂ electrode was controlled by the Li-ion diffusion in the solid phase.Secondly, Mesoporous nanocrystalline anatase TiO₂ with high surface area, well distributed pore size and high thermal stability was prepared by sol-gel method based on ILs. Long carbon-chain ionic liquids showed superior function of template and stabilizing agent. The anatase TiO₂ showed a high reversible specific capacity of 226mAh/g and kept 127mAh/g after 200 cycles at 5C.Finally, Rutile TiO₂/GE nano-composite was prepared by in-situ growth method and F-doping rutile TiO₂ was fabricated by taking TiF₄ as fluoride source. Test results showed that the electrochemical properties of rutile TiO₂, especially the rapid charge and discharge capacities were greatly improved.更多还原