二硫化钼、三氧化钼基复合材料的制备及电化学性能研究

发布时间：2018-04-24 23:24

本文选题：三氧化钼 + 二硫化钼　；参考：《陕西科技大学》2017年硕士论文

【摘要】：近年来,电动汽车和可移动电子产品的迅速发展极大地刺激了人们对于性能优异的锂离子电池的需求。人们正在积极地为锂离子电池研究和寻找更高性能的电极材料。过渡金属硫化物(TMS)由于其特殊的合金化或转化反应的储锂机制近年来吸引了越来越多的关注,相比于传统的碳负极材料,TMS对实现高比容量更为有优势。其中,二硫化钼(MoS_2),作为一种典型二维层状结构的TMS,由于其可以在一个相对较低的电位下储锂以及通过转换机制实现更高的比容量而引起了更加广泛的兴趣。然而由于本身较差的导电性以及循环过程中结构的不稳定性等问题,MoS_2作为电极材料的循环和倍率性能并不能令人满意。同样作为一种过渡金属化合物,三氧化钼(MoO_3)与MoS_2具有很多的相似之处,例如高的理论比容量,较差的循环稳定性等。针对这些问题,研究人员发现,将MoS_2和MoO_3与导电性能优良的材料结合构建特殊结构的复合材料可以很有效的改善电极材料的导电性和结构稳定性。因此,本论文主要围绕MoS_2和MoO_3,通过复合不同的纳米材料,构建了多种具有特殊结构的MoS_2和MoO_3基复合材料,以实现提高电化学性能的目的。通过多种测试手段,如XRD,XPS,Raman,SEM等对各个样品进行了表征,同时以各样品作为活性材料组装电池,测试和研究了各样品的电化学储锂性能。本文主要的研究成果如下:(1)以钼酸钠为钼源,氧化石墨烯为基体,采用一步水热法制备了MoS_2/石墨烯复合材料(MoS_2-rGO)。所制备的复合材料中,MoS_2呈花球结构,直径大约为400 nm,相对均匀地分散在石墨烯基体上。而片状结构的石墨烯则相互之间交织构成了三维的导电网络。由于这种特殊的复合结构以及导电性优异的石墨烯的引入,所制备的MoS_2-rGO复合材料表现出良好的电化学性能,当电池充放电100次之后,电池的比容量能够稳定在900 mAh/g左右。(2)以MoO_3纳米棒为无机前驱体,加入硫源,通过水热法使MoO_3与硫离子发生离子交换,制备了MoO_3@MoS_2复合材料。通过添加不同量的硫脲(1 mM,3 mM,5 mM),制备了一系列的MoO_3@MoS_2复合材料。在最佳的硫脲添加量(3 mM)时,所制备的复合材料(MoO_3@MoS_2-II)是以一维的MoO_3纳米棒为核,二维超薄的MoS_2纳米片为壳,构建的具有一维分层体系的核壳结构复合材料。在MoO_3@MoS_2-II中,MoS_2纳米片原位垂直生长在MoO_3纳米棒,反应产物一维结构的保持取决于反应体系溶剂的组成。电化学性能测试结果表明,这种由一维和二维材料构建的核壳结构复合材料具有优异的电化学性能。在电流密度为100 mA/g,300 mA/g,500 mA/g,1000 mA/g对电池进行充放电时,电池分别表现出929 mAh/g,642 mAh/g,510 mAh/g,384 mAh/g的平均放电比容量,更重要的是,在电流密度重新设置为100 mA/g时,电池的容量能够维持在868 mAh/g,说明所制备的MoO_3@MoS_2具有良好的倍率性能。在电流密度为100 mA/g进行充放电时,经过100次充放电循环之后电极材料的比容量基本保持在781 mAh/g,说明MoO_3@MoS_2-II拥有良好的循环稳定性。(3)通过磁力搅拌用氧化石墨烯将MoO_3进行包裹,制备了MoO_3@GO复合材料。电化学性能测试表明,MoO_3@GO的储锂容量相对于MoO_3有了明显地提高,首次放电容量达到1350 mAh/g,经过60次循环之后,容量保持在720 mAh/g,并且从阻抗谱中可以看出,氧化石墨烯的加入使MoO_3@GO的导电性大大提高。随后对MoO_3@GO进行了硫化。现有的测试结果表明,MoO_3@GO硫化产物(S-MoO_3@GO)可能是引入了硫的MoO_3@GO复合材料。MoO_3中引入硫之后,可能产生了氧空位,层间距增大,这些有利于电极反应过程中电荷的快速运动以及可以提高结构的稳定性,从充放电测试结果可以看出,S-MoO_3@GO在循环过程中除首次循环外,后续的容量极为稳定,同时材料也表现出极好的倍率性能。
[Abstract]:In recent years, the rapid development of electric vehicles and mobile electronic products has greatly stimulated the needs of lithium ion batteries with excellent performance. People are actively studying and looking for higher performance electrode materials for lithium ion batteries. The transition metal sulfide (TMS) is close to the lithium storage mechanism of its special alloying or conversion reaction. More and more attention has been drawn over the years. Compared to the traditional carbon negative material, TMS has the advantage of achieving high specific capacity. Among them, molybdenum disulfide (MoS_2), as a typical two-dimensional layered structure of TMS, is caused by the ability to store lithium at a relatively low potential and to achieve higher specific capacity through a conversion mechanism. However, because of its poor conductivity and the instability of the structure during the cycle, the cycle and multiplying performance of MoS_2 as an electrode material is not satisfactory. As a transition metal compound, molybdenum trioxide (MoO_3) has a lot of similarities with MoS_2, such as high theoretical specific capacity, In order to solve these problems, the researchers found that the combination of MoS_2 and MoO_3 with excellent conductive materials to build a special composite material can effectively improve the conductivity and structural stability of the electrode materials. Therefore, this paper is mainly around MoS_2 and MoO_3, through the composite of different nanomaterials. A variety of MoS_2 and MoO_3 based composites with special structures were built to improve the electrochemical performance. Various samples were characterized by a variety of testing methods, such as XRD, XPS, Raman, SEM and so on. At the same time, each sample was used as the active material to assemble the battery. The electrochemical lithium storage properties of the samples were tested and studied. The results are as follows: (1) using sodium molybdate as the molybdenum source and graphene oxide as the matrix, MoS_2/ graphene composite (MoS_2-rGO) is prepared by one step hydrothermal method. In the composite materials, MoS_2 has a flower ball structure with a diameter of about 400 nm, which is relatively evenly dispersed on the graphene matrix. The flake structure of graphene is reciprocally crossed. With the introduction of this special composite structure and the introduction of graphene with excellent conductivity, the prepared MoS_2-rGO composite exhibits good electrochemical performance. When the battery is charged and discharged for 100 times, the specific capacity of the battery can be stabilized at about 900 mAh/ G. (2) MoO_3 nanorods as inorganic precursors, MoO_3@MoS_2 composites were prepared by ion exchange between MoO_3 and sulfur ions by hydrothermal method. A series of MoO_3@MoS_2 composites were prepared by adding different amounts of thiourea (1 mM, 3 mM, 5 mM). When the optimum addition of thiourea (3 mM), the prepared composite (MoO_3@MoS_2-II) was a one-dimensional MoO_3 nanorod. Nuclear, two dimensional ultra-thin MoS_2 nanoscale is a shell, and a nuclear shell structure composite with one dimension stratified system is constructed. In MoO_3@MoS_2-II, the MoS_2 nanoscale is in situ perpendicular to the MoO_3 nanorods. The one dimension structure of the reaction product depends on the composition of the reaction system solvent. The electrochemistry test results show that this kind is from one and two. The nuclear shell structure composite constructed by the material has excellent electrochemical performance. When the current density is 100 mA/g, 300 mA/g, 500 mA/g and 1000 mA/g, the battery shows the average discharge ratio of 929 mAh/g, 642 mAh/g, 510 mAh/g, 384 mAh/g, and more importantly, when the current density is reset to 100 mA/g, The capacity of the battery can be maintained at 868 mAh/g, indicating that the prepared MoO_3@MoS_2 has a good multiplier performance. When the current density is 100 mA/g, the specific capacity of the electrode material after 100 charging and discharging cycles is basically kept at 781 mAh/g, indicating that MoO_3@MoS_2-II has a good cycle stability. (3) the use of magnetic stirring is used. The MoO_3 was wrapped and MoO_3@GO composite was prepared by the graphite oxide. The electrochemical performance test showed that the lithium storage capacity of MoO_3@GO was significantly higher than that of MoO_3. The first discharge capacity reached 1350 mAh/g. After 60 cycles, the capacity remained at 720 mAh/g, and the addition of graphene oxide made M from the impedance spectrum. The conductivity of oO_3@GO is greatly improved. MoO_3@GO is then vulcanized. The existing test results show that the MoO_3@GO vulcanization product (S-MoO_3@GO) may be the introduction of sulfur in the MoO_3@GO composite.MoO_3 with sulfur, which may produce oxygen vacancies and increase the interlayer spacing, which are beneficial to the rapid motion of the charge in the electrode reaction. The stability of the structure can be improved. It can be seen from the test results of charge and discharge that the subsequent capacity of S-MoO_3@GO is very stable except for the first cycle in the cycle process, and the material also shows excellent multiplier performance.

【学位授予单位】：陕西科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB33

【参考文献】