碳素材料储钠研究

发布时间：2018-03-15 18:32

  本文选题：二次电池　切入点：负极　出处：《中国科学院大学(中国科学院物理研究所)》2017年博士论文　论文类型：学位论文

【摘要】：随着人们对能源需求的增长和清洁能源的开发,能源储存和转化越来越受到人们的关注。二次电池因其具有较高的能量密度和功率密度等优点,适用于大规模储能。锂离子电池和钠离子电池是目前二次电池研究发展的主要研究方向。随着锂离子电池在便携式电子设备方面的应用和在电动汽车方面的推广,锂的需求量在不断增加,再加上地球上锂资源的有限性和局域性,锂的价格在不断上升。由于钠具有与锂相似的物理化学性质,储量丰富,成本低廉,因此钠离子电池在大规模储能方面具有可持续发展的优势。另一方面,由于钠离子具有比锂离子更大的离子半径(0.97?vs 0.68?),所以部分在锂离子体系中电化学性能优异的材料不能直接用于钠离子电池。探索电化学性能优异的电极材料并研究其机理对推动钠离子电池的发展和应用具有重要意义。本文研究碳材料和钛基氧化物作二次电池负极的电化学性能,并对其结构进行相应表征。以不同浓度的Na-BP-DME溶液作为还原剂将不同数量的钠离子化学嵌入进高定向热解石墨(HOPG)中,避免了电化学嵌钠时电解液分解沉积对确定样品中Na:C原子比的干扰。结合X射线衍射(XRD)、扫描透射电子显微镜(STEM)、傅里叶变换红外(FTIR)光谱和Raman光谱等结构表征分析发现,在醚类溶剂中,钠离子与溶剂分子共嵌入石墨层间,经过一系列阶的转变过程,形成三元插层化合物(GIC)。结合电感耦合等离子体光谱(ICP)和热重分析,确定出最终形成的一阶相产物的组分为Na(DME)2C26。FTIR和Raman光谱证实了钠离子、溶剂分子、石墨之间的相互作用。这种相互作用有利于保持嵌入过程中石墨结构的完整,提高实验电池的循环稳定性。此外,我们还对生成的三元GIC在空气中的稳定性进行了研究。将均匀混合的明胶与柠檬酸镁在600~900℃的惰性气氛中热解得到一系列多孔含氮碳材料。柠檬酸镁热解形成的MgO作为模板保证了所得介孔碳具有孔径分布小且均一的特点。含氮介孔碳中的氮原子主要以吡啶氮、吡咯氮和氧化氮的形式存在。石墨化氮的缺失与制备过程中柠檬酸镁的存在抑制了明胶的热交联过程有关。电化学实验结果表明,这些碳材料具有良好的电化学性能,材料的电化学性能受氮掺杂和孔结构的双重影响。在700°C下获得的介孔碳材料在首次循环中的可逆储钠容量达到360 mAh g-1,且具有良好的循环稳定性和倍率性能。通过溶胶凝胶法(sol-gel)合成了层状材料A_2TiO_3(A=Li/Na)。Li_2TiO_3和Na_2TiO_3分别具有165和274 mAh g-1的可逆储锂容量,循环稳定性较好。结合XRD和Raman光谱技术对材料结构进行分析发现,充放电过程中Li_2TiO_3的结构能够可逆地转变,Li+可能进入材料四面体间隙位置,并形成有序的排布;Na_2TiO_3在锂离子电池电解液中会发生离子交换和结构转变,形成阳离子混排的层状结构,电化学性能更好。
[Abstract]:With the increasing demand for energy and the development of clean energy, energy storage and conversion have attracted more and more attention. Secondary batteries have the advantages of high energy density and power density. Lithium ion battery and sodium ion battery are the main research direction of secondary battery research and development at present. With the application of lithium ion battery in portable electronic equipment and the popularization of electric vehicle, The increasing demand for lithium, coupled with the limited and localized nature of lithium resources on Earth, has led to a rising price of lithium, because sodium has physical and chemical properties similar to lithium, is rich in reserves and low in cost. Therefore, sodium ion battery has the advantage of sustainable development in large-scale energy storage. On the other hand, because sodium ion has a larger ion radius than lithium ion, 0.97? Vs 0.68? Therefore, some materials with excellent electrochemical performance in lithium ion system can not be directly used in sodium ion batteries. Exploring the electrode materials with excellent electrochemical performance and studying its mechanism are important for promoting the development and application of sodium ion batteries. In this paper, the electrochemical properties of carbon materials and titanium-based oxides used as anode of secondary battery are studied. The structure was characterized by using different concentrations of Na-BP-DME solution as reducing agent to embed different amounts of sodium ion chemistry into highly oriented pyrolytic graphite (HOPG). The interference of electrolytic solution decomposition deposition in determining the atomic ratio of Na:C in the sample was avoided by electrochemical sodium intercalation. The results of X-ray diffraction (XRD), scanning transmission electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were used to characterize and analyze the structure of the sample. In ether solvents, sodium ions and solvent molecules are intercalated into graphite layers, and a series of transition processes are carried out to form ternary intercalation compounds (GICs), which are combined with inductively coupled plasma spectroscopy (ICP) and thermogravimetric analysis (TGA). Na(DME)2C26.FTIR and Raman spectra show that the interaction among sodium ions, solvent molecules and graphite is beneficial to the integrity of graphite structure in the intercalation process. Improve the cycle stability of the experimental battery. In addition, We also studied the stability of ternary GIC in air. A series of porous nitrogen-containing carbon materials were obtained by pyrolysis of homogeneously mixed gelatin and magnesium citrate in an inert atmosphere of 600,900 鈩，

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