【作者】 陈卓；

【导师】 周亮；

【作者基本信息】 武汉理工大学 ， 材料科学与工程， 2019， 硕士

【摘要】 钠离子电池具有钠资源丰富、成本低、能量转换效率高等优势,在大规模储能领域中起着举足轻重的作用。推动钠离子电池技术的发展的重中之重则是开发高性能钠离子电池电极材料。二氧化钛（TiO₂）具有储量丰富、价格低廉、结构稳定性好、安全且无污染等显著优势。当用作钠离子电池负极材料时,TiO₂具有较高的理论比容量,合适的嵌钠位点和良好的循环稳定性,是一种较理想的钠离子电池负极材料。然而由于TiO₂的半导体特性,其本征导电性较差,且离子扩散能力差,需要进一步优化和改善其储钠性能。已报道的如碳包覆、元素掺杂等优化方法,多数过程繁琐复杂,采用一种简便且高效的方法来制备性能优异的TiO₂钠离子电池负极材料意义非凡。本文采用简单的喷雾热解法,设计合成了核壳结构富氧缺陷TiO₂(记作yolk@shell TiO_2-x),及其与金属Sn的复合物yolk@shell TiO_2-x/Sn两种钠离子电池负极材料。随后对其结构及微观形貌进行了测试与表征,并详细研究它们的钠离子电池性能。具体的研究内容和结果如下:（1）以水溶性的二（2-羟基丙酸）二氢氧化二铵合钛溶液（TiBALDH）作为钛源,通过喷雾热解得到TiO₂/C复合微球,在空气和氢气氛围下煅烧,形成最终产物yolk@shell TiO_2-x。（2）对材料的储钠性能进行测试,yolk@shell TiO_2-x表现出高的比容量和优异的循环性能,在50 mA g^-1电流密度下,稳定循环200圈后比容量仍有230.7mAh g^-1;在1 A g^-1电流密度下循环1000圈后容量保持率为91.7%。通过电化学阻抗分析等电化学测试以及密度泛函理论（DFT）计算来深入探究和分析了氧缺陷的引入对于TiO₂的储钠特性的影响。结果表明:TiO₂中氧缺陷的引入增加了其导电性,降低了嵌钠能垒同时促进了Na⁺的扩散。原位XRD及非原位SEM、XRD结果也进一步证明了其循环结构稳定性。（3）通过在前驱体溶液中加入锡源（甲基磺酸锡）,进一步设计合成了yolk@shell TiO_2-x与Sn的复合物,并对其结构、形貌和储钠性能进行了表征。yolk@shell TiO_2-x/Sn复合物同样表现出明显提升的比容量。在100 mA g^-1的电流密度下,其首圈放电比容量为471.4 mAh g^-1,循环120圈后,依然能够保持接近200 mAh g^-1的可逆比容量。更多还原

【Abstract】 Sodium ion batteries（SIBs）play a significant role in the field of large-scale energy storage due to the advantages of abundant sodium resources,low cost,and high energy conversion efficiency.Exploiting high-performance SIBs anode materials are the most important things to promote the development of SIBs technology.Titanium dioxide（TiO₂）has plenty of advantages:abundance,low cost,structural stability,safety,and environmental friendliness.For the specific application in SIBs,TiO₂ possesses high theoretical specific capacity,suitable Na⁺accommodation sites,and good cycling stability,which indicate that TiO₂ would be a suitable candidate as an anode material for SIBs.However,the intrinsic electrical conductivity and ion diffusivity of TiO₂ are relatively low due to its semi-conductor properties,which require further optimizations and enhancements of its sodium storage performance.Most of the previous reported methods,including carbon coating and foreign element doping,are tedious and complex.Therefore,it is of great significance to employ a facile and efficient synthetic method to obtain high-performance TiO₂ anode materials.In this thesis,two kinds of sodium ion batteries anode materials including yolk@shell structured anatase TiO₂ microspheres with rich oxygen vacancies(denoted as yolk@shell TiO_2-x)as well as its composites with tin(yolk@shell TiO_2-x/Sn)are designed and synthesized through a facile spray-pyrolysis-assisted method.Afterwards,we characterize the structure and morphology properties of the samples.The sodium storage performance of both two samples are analyzed and studied in detail.The specific research content and results are as follows:（1）Firstly,the TiO₂/C composite microspheres are obtained by spray pyrolysis using the water-soluble titanium（IV）bis（ammonium lactato）dihydroxide（TiBALDH）solution as titanium sources.Then,the TiO₂/C composite microspheres are calcined under air and hydrogen atmosphere successively to produce the final product yolk@shell TiO_2-x.（2）The sodium storage performance of the yolk@shell TiO_2-x anode are tested.The as-synthesized yolk@shell TiO_2-x demonstrates a high reversible capacity(230.7mAh g^-1 after 200 cycles at 50 mA g^-1)and remarkable long-cycling stability(capacity retention of 91.7%after 1000 cycles at 1000 mA g^-1).In the meanwhile,electrochemical measurements（such as electrochemical impedance spectroscopy analysis）and density functional theory calculations are also employed to investigate the influence of the introduction of oxygen defects on the sodium storage performance.And the results reveal that introducing oxygen vacancies in TiO₂ enhances the electrical conductivity,lowers the sodiation energy barrier,and facilitates Na⁺diffusion kinetics.The in-situ XRD,ex-situ SEM and XRD results also prove its structural stability.（3）The composites of yolk@shell TiO_2-x and tin were further designed and synthesized,which are obtained by using the simaliar spray-pyrolysis-assisted methods with adding the tin methyl sulfonate into the precursor solutions.And then we characterize their structure,morphology,and sodium storage performance.The yolk@shell TiO2-x/Sn anode also demonstrates distinct improved cycling specific capacity and stability.When tested at the current density of 100 mA g^-1,the yolk@shell TiO_2-x/Sn electrode performs a high discharge specific capacity of 471.4 mAh g^-1.The electrode can still possess a high specific capacity of²00 mAh g^-1 after 120 cycles.更多还原