【作者】 苏庆；

【导师】 王印月； 刘雪芹；

【作者基本信息】 兰州大学 ， 凝聚态物理， 2009， 博士

【摘要】 为了解决人类社会发展带来的能源需求和环境恶化的世界性问题，新能源材料的探索已经成为全球广泛关注的热点。V₂O₅材料因其独特的层状结构，不仅可以作为锂离子二次电池的正极材料，而且还是少数几种有望应用于镁电池正极的活性材料。因此，V₂O₅是一类重要的新能源材料，系统研究V₂O₅材料的制备、结构及其特性有着重要的意义。本论文通过磁控反应溅射法制备了α-V₂O₅和β-V₂O₅薄膜，利用热蒸发化学气相沉积获得了形貌多样的V₂O₅纳米材料，采用水热法得到了VO_x纳米管（VOx-NTs），并使用各种表征手段研究了V₂O₅薄膜与纳米材料的形貌、结构与形成机理。（1）V₂O₅薄膜的溅射法制备及其循环伏安特性研究研究了实验条件对α-V₂O₅薄膜结构的影响。结果表明，在氧气分压较大的环境下，容易得到层状结构较完整的α-V₂O₅薄膜。当退火温度过高时（大于550℃），α-V₂O₅结构中的钒氧双键V=O键将容易断裂，产生氧空位，使得α-V₂O₅（001）晶面坍塌。适当的沉积温度有利于α-V₂O₅薄膜结晶。系统的研究了溅射制备β-V₂O₅薄膜及其形成机理，这方面的研究目前国内外未见报道。在550℃沉积温度（40％的氧气分压）的条件下，得到了具有β-V₂O₅结构的薄膜。实验结果表明，氧气分压和沉积温度是β-V₂O₅薄膜形成的必要因素。溅射过程中，较高的沉积温度不仅导致钒氧原子具有较高的能量，而且抑制了α-V₂O₅结构的形成。在沉积温度较高，氧气分压较大的情况下，不易生成低价态的钒氧化合物，而是有利于β-V₂O₅薄膜的形成。在合适的沉积温度（500℃）下可以得到α-和β-V₂O₅两相共存的薄膜，经过退火后α相将转变为β相。在单晶硅、石英、玻璃和ITO衬底上均可以生长β-V₂O₅薄膜。报道了β-V₂O₅薄膜的循环伏安特性，这对探索β-V₂O₅薄膜的电化学应用有着积极的意义。在ITO上分别制备了α-和β-V₂O₅薄膜，并对其循环伏安性质进行研究。结果表明，α-V₂O₅薄膜具有电化学可逆性，Li⁺和Mg²⁺均能在α-和β-V₂O₅薄膜中可逆的嵌入／脱嵌。在没有水存在的Mg（ClO₄）₂／PC溶液中，Mg²⁺在V₂O₅中的循环性能不稳定，这可能是Mg²⁺的电荷密度较大，嵌入过程中，使V₂O₅的结构发生不可逆畸变。（2）不同形貌V₂O₅纳米材料的热蒸发化学气相沉积（CVD）制备及其生长机理在低真空（约1Torr）650℃下，直接加热VO（acac）₂粉末制备了V₂O₅纳米片。这是一种简单有效制备V₂O₅纳米片的方法。加热VO（acac）₂粉末，在不同温度区域得到了各种形貌的VO_x材料，包括V₂O₅纳米棒和VO_x微米球。不同生长区域中温度的差异，使得钒氧化合物中V⁵⁺／V⁴⁺的含量比例有所不同，最终引起VO_x形貌的变化。将蒸发源VO（acac）₂粉末和V₂O₅的生长衬底分别安置于低温区和高温区，得到了V₂O₅纳米线和V₂O₅纳米球。我们提出了以金属有机物为蒸发源的化学气相生长各种纳米材料的机理。V₂O₅纳米线和纳米球的形成属于两个不同的形成机理：前者是由VO（acac）₂分解后生成的各种钒氧离子团成核、生长所形成；后者是由源蒸汽在传输过程中直接化合生成。（3）VOx纳米管（VOx-NTs）的水热法制备及其循环伏安特性。以V₂O₅粉末、H₂O₂溶液和十二胺乙醇溶液为原料制备纳米管，并研究了pH值对纳米管形成的影响。结果表明，强酸条件下，得到了V₆O₁₃结构的微米片和微米带。碱性条件下合成了VO_x-NTs。水热反应过程中，前驱液的酸碱性，一方面与V₂O₅·nH₂O溶胶的形成密切相关，另一方面对十二胺的质子化产生影响。强酸性条件阻碍了纳米管的形成，而在碱性条件下会促进V₂O₅层状结构的生成，有利于纳米管的生长。延长V₂O₅·nH₂O与十二胺乙醇溶液的搅拌时间，将V₂O₅·nH₂O与十二胺的摩尔比增大到1：1，提高了纳米管的产率。将V₂O₅粉末、去离子水和十二胺乙醇溶液（V₂O₅与十二胺摩尔比为1：1）混合制备V₂O₅·nH₂O／十二胺悬浊液，制备出了质量较好的VO_x-NTs。在pH=8和10时，得到的纳米管长度达到几微米。循环伏安测试结果表明，相对于片状的VO_x，VO_x-NTs表现出较好的Li⁺嵌入／脱嵌性能。更多还原

【Abstract】 In order to solve the global problems of the energy demand and environmentpollution from the human societal development,exploiting the new energy resource isan important hot point of global investigating field.Vanadium pentoxide （V₂O₅）materials with the special layer structure are not only the cathode material of Li ionrechargeable battery,but also one of the rare active materials that are hoped to use forthe active materials in the cathode of Mg rechargeable battery.Therefore,V₂O₅ is akind of important new energy materials and it is significant to study the preparation,structure and properties of V₂O₅In this thesis,α-V₂O₅ andβ-V₂O₅ films were prepared using sputtering,VOxwith various morphologies were formed by thermal evaporation chemical vapordeposition （CVD）and VOx-NTs were synthesized through hydrothermal treatment.The morphologies,structure and formation mechanism of V₂O₅ films andnanomaterials were studied.（1）V₂O₅ films were prepared by sputtering and electrochemical properties werestudied.The influence of conditions on the structure ofα-V₂O₅ films was investigated.α-V₂O₅ films with perfect layer structure were easily obtained at the high oxygenpartial pressure.As the annealing temperature is too high （over 550℃）,the V=Obonds can be broken,which leaded to the oxygen vacancies and the collapse ofα-V₂O₅（001）planes.A proper depositing temperature is favorable for thecrystallization ofα-V₂O₅ films.The preparation and formation mechanism ofβ-V₂O₅ films were studiedsystemically,which has not been reported.β-V₂O₅ films were formed at 550℃（40%oxygen partial pressure）.It is revealed that the depositing temperature and oxygenpartial pressure are the needed factor forβ-V₂O₅ films.During the sputtering process,high depositing temperature gives the V and O atoms strong energy to move and keeps from the formation ofα-V₂O₅ structure.The vanadium oxides with low valencestate are not formed in the high oxygen partial pressure,butβ-V₂O₅.In the medialdepositing temperature,films withα-andβ-V₂O₅ were obtained,andαphase cantransform toβphase by annealing.β-V₂O₅ films can be prepared on Si,quartz,glassand ITO substrates.The electrochemical properties of V₂O₅ films deposited on ITO substrates werestudied by cyclic voltammograms.The results revealed thatα-andβ-V₂O₅ filmsshowed electrochemical reversible to Li⁺ and Mg²⁺.In the inaqueous Mg（ClO₄）₂/PCsolution,the reversible properties of V₂O₅ were poor for Mg²⁺,might result form thestructure distortion of V₂O₅ caused by the insertion of Mg²⁺.（2）Different vanadium oxides were prepared by thermal evaporation CVD usingVO（acac）₂ powder as V source and formation mechanism were investigated.In the low vacuum and at 650℃,V₂O₅ nanosheets were obtained by directlyheating VO（acac）₂.This is a simple and effective way for preparation V₂O₅nanosheets.Heating VO（acac）₂ at 650℃,VOx with various morphologies were formed atdifferent temperature zones.The content ratio of V⁵⁺/V⁴⁺in VO_x,caused by thevarious growth temperatures,was the main factor for the different morphologies.Planting the VO（acac）₂ and the substrates in the low and high temperaturezones respectively,V₂O₅ nanowires and V₂O₅ nanospheres were prepared.Themechanism was suggested for the nanomaterials formation using metal organic asprecurs during thermal evaporation CVD process.The formation of V₂O₅ nanowireand V₂O₅ nanospheres from two different mechanism:the former comes from thenucleation and growth of VO ion groups which were produced by the decompositionand oxidation of VO（acac）₂ powder;the latter were formed directly through thedecomposition of VO（acac）₂ powder during the transfer process.（3）VOx nanotubes （VOx-NTs）were prepared by hydrothermal treatment andelectrochemical properties were studied.VOx-NTs were prepared by hydrothermal treatment using V₂O₅powder,H₂O₂and dodecylamine/ethanol solution.The relationship between the formation of VO_x-NTs and pH value was studied.It revealed that nanosheets and nanobelts withV₆O₁₃structure were found under strong acid conditions.Under alkaline conditions,VO_x-NTs were formed.However,other products including sheets and belts were alsoobtained.During the hydrothermal treatment process,the pH value is important to theformation of VO_x-NTs.On one hand,the creation of V₂O₅·nH₂O sol depends on thepH value;on the other hand,it can influence the dodecylamine’s proponation.Thestrong acid conditions disturbed the formation of VO_x-NTs.Prolong the stirring time of V₂O₅·nH₂O sol and dodecylamine/ethanol solution,meanwhile increasing the mol ratio of V₂O₅·nH₂O and dodecylamine to 1:1,samplescontained a great deal of VOx-NTs were synthesized.Using V₂O₅ powder,deionized water and HAD/ethanol solution as source,desirable VO_x-NTs were prepared.When the pH value was adjusted as high as 8 or 10,VOx-NTs with several micrometers were synthesized.The results from cyclic voltammograms showed that the Li⁺ can insert/deinsert inVO_x-NTs better than that in the VO_xsheet.更多还原