过渡金属化合物的设计合成及其在锂离子电池负极材料中的应用

发布时间：2018-06-09 14:02

本文选题：过渡金属硫化物 + 过渡金属氧化物　；参考：《东北师范大学》2017年硕士论文

【摘要】：作为新型储能设备,锂离子电池的研制备受关注,成为各国研究者的研究热点。为了满足社会发展的需要,锂离子电池应具有高的容量,长的循环寿命,良好的倍率性能。然而,在商业化负极材料中占主要地位的石墨,比容量低(372mAh g-1),远远不能满足社会需求。因此,开发容量高,循环稳定好,倍率性能优异的负极材料迫在眉睫。迄今为止,研究者们已开发出各种各样的负极材料,如合金类材料,碳材料,过渡金属氧化物,过渡金属硫化物等。其中过渡金属氧化物和过渡金属硫化物因其高的理论比容量备受研究者的青睐。MoS2作为典型的过渡金属硫化物,具有类石墨烯的二维结构,其独特的结构使其具有优异的电化学性能。但是MoS2导电性能差,在实际应用过程中容易团聚。这些不足之处都限制着它的应用。此外,过渡金属氧化物(Co3O4)具有超高的理论比容量,几乎是石墨的三倍,但是体积膨胀大,在充放电过程中,引起电极材料粉碎,导致容量迅速衰减是它的致命缺点。另外,Co3O4的导电性能差也是导致其性能不佳的主要因素。针对上述问题,有效的解决方案主要包括制备各种形貌的纳米材料以及合成复合材料,从而提高材料的电化学性能。本文主要设计合成结构新颖的MoS2和Co3O4,并成功使用碳材料对其进行修饰,通过两者之间的协同作用,来提高材料的电化学性能。主要研究包括:(1)采用一步水热高温处理的方法合成微纳结构的MoS2/N-C复合材料。MoS2纳米晶镶嵌在多孔的氮掺杂的体相碳材料中,形成微纳结构;使用生物材料蛋黄作为碳源,环境友好,成本低廉,合成过程简单,可实现大规模生产。合成的复合物这种特殊的结构抑制了MoS2在充放电过程中的团聚,纳米化的MoS2暴露出更多的活性位点,碳材料的引入提高了材料的导电性。研究结果表明MoS2/N-C复合材料的倍率性能以及循环稳定性远高于纯MoS2。当电流密度为100 mA g-1时,MoS2/N-C复合材料循环100圈之后其容量仍有805 mAh g-1,而纯MoS2则不到100 mAg-1。在电流密度为500 mA g-1的高电流密度下循环500圈之后容量可高达630 mA h g-1,展现出优异的循环性能。(2)采用一步水解钴盐高温处理的方法合成Co3O4/rGO的复合材料。该材料的制备过程简单,安全性能高。所得的Co3O4纳米颗粒沉积在还原石墨烯片上,材料的比表面积大,活性材料尺寸小,与电解质接触的活性位点增多,与石墨烯形成复合材料,石墨烯具有特殊性质可以缓解材料在循环过程中产生的体积膨胀,提高材料导电性,从而改善材料的电化学性能。研究结果表明Co3O4/rGO的复合材料相较于纯Co3O4其循环稳定性,倍率性能以及容量都得到了大幅度提高。电流密度为100 mA g-1时,Co3O4/rGO复合材料的首圈放电容量1217.3 mAh g-1,充电容量为805.6 mAh g-1,库伦效率为66.2%,循环130圈之后容量维持在1095.1mAh g-1,性能远远优于纯Co3O4。
[Abstract]:As a new type of energy storage equipment, the development of lithium ion battery has attracted much attention. In order to meet the needs of social development, lithium ion batteries should have high capacity, long cycle life and good rate performance. However, graphite, which dominates the commercial anode materials, has a low specific capacity of 372mAh g-1, which is far from satisfying the social needs. Therefore, it is urgent to develop negative electrode materials with high capacity, good cycle stability and excellent rate performance. So far, researchers have developed a variety of negative electrode materials, such as alloy materials, carbon materials, transition metal oxides, transition metal sulfides and so on. Among them, transition metal oxides and transition metal sulphides are favored by researchers because of their high theoretical specific capacity. As typical transition metal sulphides, the transition metal oxides and transition metal sulphides have the two-dimensional structure of graphene. Its unique structure makes it have excellent electrochemical performance. But MoS2 has poor conductivity and is easy to agglomerate in practical application. These shortcomings limit its application. In addition, the transition metal oxide (Co _ 3O _ 4) has a high theoretical specific capacity, almost three times of that of graphite, but it has a fatal disadvantage of large volume expansion, which causes the electrode material to crush and lead to rapid capacity decay during charging and discharging. In addition, the poor conductivity of Co 3 O 4 is also the main factor leading to its poor performance. To solve the above problems, the effective solutions include the preparation of nano-materials with various morphologies and the synthesis of composite materials, so as to improve the electrochemical properties of the materials. In this paper, MoS2 and Co _ 3O _ 4 with novel structures were designed and synthesized, and the carbon materials were successfully modified to improve the electrochemical properties of the materials by synergistic action between them. The main research contents include: (1) Synthesis of MoS _ 2 / N _ C composite with micro-nano structure by one-step hydrothermal high-temperature treatment. MoS _ 2 nanocrystalline is embedded in porous nitrogen-doped bulk carbon material to form micro-nano structure; egg yolk is used as carbon source. Environmental friendly, low cost, simple synthesis process, can achieve mass production. The special structure of the synthesized complex inhibits the aggregation of MoS2 during charge and discharge. The nano-MoS2 exposes more active sites and the introduction of carbon materials improves the conductivity of the materials. The results show that the ratio properties and cyclic stability of MoS _ 2 / N-C composites are much higher than those of pure MoS _ 2 / N-C composites. When the current density is 100mAg ~ (-1), the capacity of MoS _ 2 / N-C composite is still 805 mAh g ~ (-1) and less than 100mAg-1 for pure MoS _ 2 / N-C composite material. At a high current density of 500mAg ~ (-1), the capacity of Co _ 3O _ 4 / rGO composites can be as high as 630mA 路h ~ (-1) after 500 cycles, showing excellent cycling performance.) Co _ 3O _ 4 / rGO composites were synthesized by one-step hydrolysis of cobalt salt at high temperature. The preparation process of the material is simple and the safety performance is high. The resulting Co _ 3O _ 4 nanoparticles were deposited on the reduced graphene sheet with large specific surface area, small active material size, increased active sites in contact with electrolyte, and formed a composite material with graphene. Graphene has special properties which can alleviate the volume expansion and improve the electrical conductivity of the materials during the cycle, thus improving the electrochemical properties of the materials. The results show that the cyclic stability of Co _ 3O _ 4 / rGO composite is much higher than that of pure Co _ 3O _ 4. When the current density is 100mAg ~ (-1), the first-loop discharge capacity is 1217.3 mAh g ~ (-1), the charge capacity is 805.6 mAh g ~ (-1), and the Coulomb efficiency is 66.2 when the current density is 100mAg ~ (-1). The capacity of the composite is maintained at 1095.1mAh g ~ (-1) after 130th cycle, which is much better than that of pure Co _ 3O _ 4.
【学位授予单位】：东北师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB33;TM912

【参考文献】