【作者】 杨帆；

【导师】 孙立涛；

【作者基本信息】 东南大学 ， 微电子与固体电子学， 2020， 硕士

【摘要】 目前,越来越严峻的环境污染问题促使人们将目光投向清洁能源及其有效转化和存储技术的研究。锂离子电池因其优异的性能而在移动设备和电动汽车等领域具有明显的优势地位。然而,锂元素的大规模低成本应用受到其储量并不丰富这一特点的限制。钠离子和锂离子的理化性质接近,且钠元素储量丰富,成本低,因此钠离子电池是人们关注的锂离子电池的补充选项之一。在目前应用的负极材料中,石墨最为常见,但是其存在生成SEI膜的问题,从而带来安全隐患。二氧化钛负极材料较高的充放电电位使得其具有良好的循环安全性。二氧化钛负极材料也可应用于钠离子电池系统。宏观研究往往难以深入解释材料在锂/钠离子输运过程中的机理,而透射电子显微镜技术则可以从微观角度诠释其机理。本文以原位透射电子显微镜电学实验平台为基础,探究了不同结构二氧化钛材料锂及钠离子的输运机理。1)研究了锐钛矿二氧化钛纳米线锂离子的输运机制。实验发现锐钛矿二氧化钛纳米线基本保持了原有的形态,体积膨胀较小,锐钛矿纳米线嵌锂过程经历了从四方相锐钛矿TiO₂（I41/amd）到正交相Li_0.5TiO₂（Imma）再到四方相Li TiO₂（I41/amd）的相变;2)研究了单斜晶系的TiO₂（B）纳米线锂离子的输运机制,和锐钛矿二氧化钛纳米线嵌锂的过程中形貌变化类似,TiO₂（B）纳米线形态基本保持原貌,体积膨胀也较小,通过选区电子衍射原位观察TiO₂（B）纳米线的结构变化,发现其经历了TiO₂（B）到Li_0.5TiO₂（B）再到Li_0.9TiO₂（B）的转变;3)研究了TiO₂（B）纳米线嵌钠行为,与嵌锂实验相比,嵌钠时纳米线的体积变化更加明显,钠离子嵌入TiO₂（B）时,会生成Na₂TiO₃和Na₂O,另外,钠离子嵌入时还可能发生歧化反应,生成六方相金属钛单质。没有电化学反应活性的Na₂TiO₃的生成可能是TiO₂（B）负极钠离子电池容量损失的原因之一。更多还原

【Abstract】 At present,more and more serious environmental pollution problems make people focus on the research of clean energy and its effective transformation and storage technology.Due to its excellent performance,lithium ion battery has obvious advantages in the field of mobile devices and electric vehicles.However,the large-scale and low-cost application of lithium is limited by the fact that its reserves are not abundant.The physical and chemical properties of sodium ion and lithium ion are similar,and sodium element is rich in reserves and low in cost.Therefore,sodium ion battery is one of the complementary options of lithium ion battery.At present,graphite is the most common anode material,but it has the problem of SEI film formation,which brings security risks.The high charge-discharge potential of titanium dioxide makes it have good cycle safety.Titanium dioxide anode material can also be used in sodium ion battery system.It is difficult to explain the mechanism of lithium/sodium transport in the macroscopic study,while the transmission electron microscopy can explain the mechanism from the microscopic point of view.In this thesis,the transport mechanism of lithium and sodium ions in titanium dioxide materials with different structures has been studied based on the in-situ TEM electrical experiment platform.1)The transport mechanism of lithium ion in anatase TiO₂nanowires was studied.It is found that the anatase TiO₂nanowires keep their original shape and have a small volume expansion.The lithium intercalation process of anatase nanowires has experienced reversible phase transition from tetragonal anatase TiO₂（I41/AMD）to orthorhombic Li_0.5TiO₂（imma）to tetragonal Li TiO₂（I41/AMD）;2)the transport mechanism of lithium ion in Monoclinic TiO₂（B）nanowires and anatase TiO₂nanowires have been studied In the process of lithium intercalation,the morphology change of TiO₂（B）nanowires is similar as anatase TiO_2..The morphology of TiO₂（B）nanowires basically is the same,and the volume expansion is also small.The structural changes of TiO₂（B）nanowires are observed in situ by selected area electron diffraction,and it is found that they undergo the transformation from TiO₂（B）to Li_0.5TiO₂（B）and then to Li_0.9TiO₂（B）;3)the sodium intercalation behavior of TiO₂（B）nanowires is studied.Compared with the lithium intercalation experiment,the volume changes of TiO₂（B）nanowires during sodium intercalation It is more obvious that when the sodium ion is embedded in TiO₂（B）,Na₂TiO₃and Na₂O will be formed.In addition,the disproportionation reaction may occur when the sodium ion is embedded,and the hexagonal phase metallic titanium will be formed.The formation of Na₂TiO₃without electrochemical reaction activity may be one of the reasons for the capacity loss of TiO₂（B）negative sodium ion battery.更多还原