锑基纳米复合材料的制备及储钠性能研究

发布时间：2017-12-26 21:28

本文关键词：锑基纳米复合材料的制备及储钠性能研究　出处：《西南大学》2017年博士论文　论文类型：学位论文

【摘要】：为了满足人们对小型化电子器件的需求并解决混合动力系统的能源储存问题,目前各种能源储存器件已经被研究并广泛地应用于日常生活和工业化生产中。其中,钠离子电池作为一种新型的储能器件,其采用的金属钠元素具有资源丰富、价格低廉且分布广泛地天然优势,因此有望成为锂离子电池的潜在替代者来实现大规模低成本的商业化生产。尽管金属锂和钠同处在第一主族,使它们具有相似的化学性质,但是钠离子相比于锂离子具有更大的半径和摩尔质量使的它在刚性材料的可逆脱嵌和动力学过程受到了阻碍。因此选择合适的电极材料和设计新型的电极结构来构建钠离子电池的电极能够有效的促进钠离子电池的快速发展。随着纳米技术的快速发展带来了一系列新型的纳米材料如金属氧化物、硫化物、硒化物等,由于它们具有较大的理论容量而被广泛的研究,然而上述材料在循环过程中较差的电子导电率和严重的结构坍塌影响了它们的电化学性能。因此,如何进一步的优化和开发新型的纳米复合材料去实现高容量、长寿命的钠离子电池是该领域的重要研究课题。本论文以锑基纳米材料为依托,通过利用碳包覆或者与二维石墨烯复合等手段制备了四种不同的纳米复合材料,改善了锑基材料的导电性并有效抑制了因钠离子脱嵌导致的体积膨胀等不利因素,实现了大容量、长寿命和高倍率的储钠能力。在此基础上,合理的构建和设计了新概念的电极结构使其作为无粘结剂的电极,系统研究了电极结构对纳米材料的电化学性能的影响。主要的研究内容和结果如下。1.金属锑由于具有大的理论容量而被广泛研究,但是由于钠离子的可逆脱嵌会造成材料的结构塌陷表现出了快速的容量丢失。本研究利用静电纺丝技术和高温烧结方法制备了碳包覆的锑纳米复合纤维,并通过调控不同Sb(CH3COO)3前驱体的含量得到了不同形貌的纳米纤维。实验中探讨了前驱体含量对材料形貌和电化学性能的影响,研究发现,当Sb(CH3COO)3的含量为1 mmol时,制备的C@Sb纳米纤维内部锑纳米颗粒均匀的分散且粒子之间具有一定的间隙,从而实现了在充放电过程中对锑纳米结构的有效保护。同时纳米纤维之间构建的网状结构能够很好的促进电子的快速传递并改善钠离子的扩散动力学,缩短了钠离子插入的路径。电化学结果表明,C@Sb纳米纤维表现出了优异的循环稳定性,在1 A g~(-1)的电流密度下经过700圈循环后放电容量仍然保持在386.3 m Ah g~(-1),容量保留率为73.8%(相对于第二圈容量),在5 A g~(-1)下循环4000圈后容量保持在273 m Ah g~(-1)伴随着60%的容量保留率。同时,C@Sb电极也表现出了极好的倍率性能,即使在20 A g~(-1)的电流密度下,仍然拥有高达272.1 m Ah g~(-1)的容量。所以在高性能钠离子电池金属锑负极中,一维的纳米复合纤维结构是提高储钠性能十分有效的手段之一。2.金属氧化物由于具有价格低廉、容易获得等特点被广泛研究,但是较差的电子导电率和大的体积膨胀会限制它的实际应用。在本研究中,采用已经制备的聚甲基丙烯酸刷功能化修饰氧化石墨烯表面构建了独特的三维框架结构,接着通过水热反应制备了聚合物刷修饰的graphene@Sb2O3粒子(polymer brush modified graphene@Sb2O3,PMGS)。将制备的PMGS电极材料作为钠离子电池负极时表现出了优异的循环稳定性和高的比容量。在100 m A g~(-1)循环120圈后,放电比容量为442 m Ah g~(-1),分别是r GO@Sb2O3和纯的Sb2O3电极容量的2.3和8.2倍,而且PMGS电极在400 m A g~(-1)的电流密度下循环200圈后容量约为220 m Ah g~(-1)。此外,PMGS也展现了更优的倍率性能,在800 m A g~(-1)的电流密度下仍然具有160 m Ah g~(-1)的放电容量,是r GO@Sb2O3和纯的Sb2O3电极容量的1.4和5.7倍。通过交流阻抗谱(EIS)证明了PMGS电极的在上述三种电极中具有最快速的钠离子扩散动力学。上述优异的储钠性能主要是由于聚合物刷功能化修饰石墨烯后不仅降低了材料的颗粒尺寸,增加了纳米粒子与电解液之间的接触面积,而且也能够改善材料的机械性能并阻止Sb2O3纳米粒子在充放电过程中的团聚从而提升了PMGS的储钠能力。此外,我们借助XRD,XPS和TEM对PMGS材料在不同初始充放电态的相转变过程进行了系统的研究,结果显示该材料在充放电过程中遵循转换和合金反应机理。3.众所周知,将纳米材料与石墨烯复合能有效的改善材料的电子导电率,但是石墨烯作为电极材料的组成单元不能够满足容量的最大化,同时它较低的振实密度和体积容量限制了复合物材料的储钠性能。在本工作中,我们使用尿素作为氮源,采用一步水热反应制备了网状的氮掺杂的graphene@Sb2Se3复合物(NGS),并通过相同的方法制备了未掺杂氮的graphene@Sb2Se3(GS)和纯的Sb2Se3纳米棒作为对照组实验。相比于GS和纯的Sb2Se3材料,NGS材料拥有三维的网状结构,使得它能够与电解液充分的接触,实现快递的电荷和离子传输。电化学测试表明,NGS的整个电化学过程由离子扩散所控制,并且作为钠离子电池负极时拥有好的循环稳定性和倍率性能。在100 m A g~(-1)时,循环50圈后放电容量为548.6 m Ah g~(-1),分别是GS和纯的Sb2Se3电极容量的1.6和2.8倍。即使在1.5 A g~(-1)的电流密度下,NGS电极的容量仍然达到了337 m Ah g~(-1),分别是GS和Sb2Se3电极容量的3和12.5倍。此外,通过交流阻抗谱分析(EIS)得到NGS的钠离子扩散系数分别是GS和纯的Sb2Se3的3和8.5倍,由此说明了网状的NGS材料能够促进快速的钠离子传输。优越的电化学性能主要归因于氮掺杂的石墨烯拥有更加无序的碳结构能够为钠离子插入的提供更多位点从而拥有更大的可逆容量,同时相互交错的网状结构明显的改善了材料的电子和离子电导率,而且能够持续的缩短钠离子插入到Sb2Se3纳米棒内部的距离,从而表现出快速的界面电子速率。此外,大量的石墨烯片覆盖在Sb2Se3纳米棒上面能够提供一个柔性的缓冲空间去调节体积膨胀,从而保持了纳米结构的完整性。4.为了有效的解决充放电过程中钠离子扩散的热力学和动力学问题,本工作中,首先采用水热法合成了Sb2S3/CNT复合物,然后用简单的电化学沉积和浸渍涂覆的方法制备了(Sb2S3/CNT@RGO)n的多层电极。为了研究不同层数对于Sb2S3/CNT复合材料电化学性能的影响,实验制备了不同层数(2,3,4,5和6层)的电极并对它们的电化学性能进行了测试。结果表明,当电极层数为3层时,电极表现出了最好的比容量和比能量。将制备的(Sb2S3/CNT@RGO)3电极作为钠离子电池负极时,在400 m A g~(-1)时循环100圈后拥有604 m Ah g~(-1)的放电比容量,是传统涂覆制备的块状Sb2S3电极(Sb2S3/CNT:carbon black:binder=7:2:1)容量的7.5倍。同时,它具有更加显著的倍率性能,在3 A g~(-1)的电流密度下充放电时,容量为400 m Ah g~(-1),是块状Sb2S3电极容量的6.1倍。同时交流阻抗谱显示,多层的(Sb2S3/CNT@RGO)3电极的钠离子扩散系数是块状Sb2S3电极的5.3倍,由此证明多层的电极结构能够促进快速的钠离子传输。优异的储钠性能主要是由于多层的电极结构具有快速的电荷转移速率、高的钠离子迁移率和高的质量传输效率,从而明显的改善热力学和动力学限制。综上所述,通过有效的设计与优化电极材料或者合理的构建电极结构可以极大的改善电极材料的导电性和因钠离子脱嵌造成的结构塌陷,从而显著的提高电极材料的钠储存性能。
[Abstract]:In order to meet the needs of miniaturized electronic devices and solve the problem of energy storage in hybrid power system, various energy storage devices have been researched and widely applied in daily life and industrial production. Among them, sodium ion battery, as a new type of energy storage device, has the advantages of abundant resources, low cost and widely distributed natural resources. Therefore, it is expected to become a potential substitute for lithium ion battery to achieve large-scale and low-cost commercial production. Although lithium and sodium are located in the first main family and give them similar chemical properties, sodium ions are hindered by the greater radius and molar mass of sodium ions than that of lithium ions, resulting in the reversible deintercalation and dynamic process of rigid materials. Therefore, choosing suitable electrode materials and designing new electrode structure to build the electrode of sodium ion battery can effectively promote the rapid development of sodium ion battery. With the rapid development of nanotechnology has brought a series of new nano materials such as metal oxides, sulfides, selenides, etc., because of their large capacity theory has been widely studied, however, the poor electronic conductivity material in the circulation process and the severity of the collapse of the structure affects their electrochemical properties. Therefore, how to further optimize and develop new nanocomposites to achieve high capacity and long life sodium ion battery is an important research topic in this field. In this paper, antimony based nano materials as the basis, through the use of carbon coated or two-dimensional graphene composite was prepared by means of four kinds of nano composite materials of different, improve the electrical conductivity of antimony based materials was inhibited by sodium ion intercalation due to volume expansion due to unfavorable factors such as the implementation of big capacity, long life life and high rate of sodium storage capacity. On this basis, the electrode structure of the new concept was reasonably constructed and designed to make it an electrode without binder. The influence of electrode structure on the electrochemical performance of nanomaterials was systematically studied. The main research content and results are as follows. 1., metal antimony has been extensively studied due to its large theoretical capacity. However, due to the reversible deintercalation of sodium ions, the structure collapse of materials shows fast capacity loss. In this study, carbon coated antimony nanocomposite fibers were prepared by electrospinning and high temperature sintering. Different morphologies of nanofibers were obtained by regulating the content of precursors of different Sb (CH3COO) 3. The experiment is to investigate the effect of precursor concentration on the morphology and electrochemical properties of materials research found that when Sb (CH3COO) 3 was 1 mmol, with a certain gap between the dispersion and particle C@Sb nanofiber internal antimony nanoparticles prepared by a uniform, so as to realize the effective protection of the charge and discharge process antimony nano structure. Meanwhile, the network structure constructed by nanofibers can promote the rapid transmission of electrons, improve the diffusion kinetics of sodium ions, and shorten the path of sodium ion insertion. The electrochemical results show that C@Sb nanofibers exhibited excellent cycle stability, in 1 A g~ (-1) of the current density after 700 cycles after the discharge capacity remained at 386.3 m Ah g~ (-1), the retention rate of capacity is 73.8% (compared to second laps in the 5 A capacity), g~ (-1) under after 4000 cycles the capacity retention at 273 m Ah g~ (-1) with 60% capacity retention rate. At the same time, the C@Sb electrode also showed excellent multiplier performance. Even under the current density of 20 A g~ (-1), it still had a capacity of up to 272.1 m Ah g~ (-1). Therefore, in the metal antimony anode of high performance sodium ion battery, one dimensional nanocomposite fiber structure is one of the most effective ways to improve the performance of sodium storage. 2., metal oxide has been widely studied due to its low cost and easy access. However, poor electron conductivity and large volume expansion will limit its practical application. In this study, which was prepared by acrylic brush functionalized graphene oxide surface to construct a three-dimensional frame structure unique, then prepared through hydrothermal reaction of graphene@Sb2O3 particles modified polymer brushes (polymer brush modified graphene@Sb2O3, PMGS). As the negative electrode of the sodium ion battery, the prepared PMGS electrode exhibits excellent cyclic stability and high specific capacity. After 120 cycles of 100 m A g~ (-1) cycle, the discharge specific capacity is 442 m Ah g~ (-1), which is 2.3 and 8.2 times of R GO@Sb2O3 and pure Sb2O3 electrode capacity, respectively, and the capacity of the Ah electrode is 220 220, when the current density of 400 electrode is 400. In addition, PMGS also exhibits better rate performance. It has 160 m Ah g~ (-1) discharge capacity at 800 m A g~ (-1) current density, which is 1.4 and 5.7 times of R GO@Sb2O3 and pure -1 electrode capacity. Through the AC impedance spectroscopy (EIS), it is proved that the PMGS electrode has the fastest diffusion kinetics of sodium ion in the three kinds of electrodes. The excellent performance of sodium storage is mainly due to polymer brush functionalization of graphene can not only reduce the particle size of the material, increase the contact area between the nanoparticles and the electrolyte, but also can improve the mechanical properties of materials and prevent Sb2O3 nanoparticles discharge in the process of agglomeration in the charge so as to enhance the storage ability of PMGS sodium. In addition, we have systematically studied the phase transformation process of PMGS materials in different initial charge and discharge state by means of XRD, XPS and TEM. The results show that the conversion and alloy reaction mechanism are followed during charging and discharging. 3. as everyone knows, the nano material composite with graphene can effectively improve the electronic conductivity of the material, but Shi Moxi as a unit of electrode materials can not meet the maximum capacity, and low tap density and volume limits the storage performance of sodium composite materials.
【学位授予单位】：西南大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM912

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