尖晶石锰酸锂及其化合物的表面修饰

发布时间：2019-02-25 07:41

【摘要】：随着资源和环境危机的加剧，锂离子电池正极材料受到了更广泛的关注，越来越多的研究人员也致力于正极材料的合成和改进。总的来说，正极材料的改进主要从两个方面着手：一是化学方法，通过掺杂或表面包覆等手段减小材料和电解液的直接接触面积，，从而改善电极的放电比容量、倍率性能和循环性能，尤其是高温循环性能；二是物理方法制备混合电极，利用不同种类正极材料的协同作用稳定晶体结构，从而达到改善电极电化学性能、结构和热稳定性的目的。本文主要围绕尖晶石LiNi0.5Mn1.5O4和LiMn2O4两种材料进行改性，主要内容包括以下几个方面：第一章：根据材料中金属种类的不同对电池正极材料进行了分类，重点介绍了文章中主要涉及到的三种材料（LiNi0.5Mn1.5O4、LiMn2O4和LiNiO2）的合成方法、结构特征、容量衰减因素和存在的问题，并对三种材料的包覆、掺杂和物理混合等改性研究进行了归纳总结。第二章：采用二次干燥共沉淀法合成尖晶石LiNi0.5Mn1.5O4，并通过溶胶-凝胶法对其进行表面包覆改性，制备出LiNi0.5Mn1.5O4表面存在均匀LiCoPO4包覆层的正极材料。提出了采用工作电压与本体材料接近的活性电池材料作为包覆物质的概念，通过XRD、SEM、TEM、交流阻抗测试等手段对材料进行了表征，实验结果研究表明，2wt%LiCoPO4包覆层的存在，明显地改善了电池材料的电化学性能和热稳定性。第三章：在前一章实验内容的基础上改变包覆方法，在前驱体表面包覆Co3(PO4)2，然后与LiOH H2O混合，经过一步烧结制备出LiCoPO4包覆的LiNi0.5Mn1.5O4，透射电镜结果证明了包覆层的存在，而蓝电测试结果表明材料经包覆改性后性能得到了提高。第四章：采用溶胶-凝胶法分别制备了层状结构的LiNiO2和尖晶石结构的LiMn2O4，按照质量比为1:9的比例混合制备混合电极。利用XRD等手段证明了电池材料的成功制备，并对混合、单一电极分别进行了电化学性能测试。结果表明，与单一LiMn2O4电极相比，混合电极表现出更高的放电容量，更优异的倍率性能和循环稳定性。
[Abstract]:With the aggravation of resource and environment crisis, more and more researchers focus on the synthesis and improvement of cathode materials for lithium-ion batteries. In general, the improvement of cathode materials mainly starts from two aspects: one is chemical method, which reduces the direct contact area between material and electrolyte by doping or surface coating, thereby improving the specific discharge capacity of the electrode. Double rate performance and cycle performance, especially high temperature cycle performance; Secondly, the mixed electrode was prepared by physical method, and the crystal structure was stabilized by the synergistic action of different kinds of cathode materials, so as to improve the electrochemical performance, structure and thermal stability of the electrode. In this paper, two kinds of spinel LiNi0.5Mn1.5O4 and LiMn2O4 were modified. The main contents include the following aspects: chapter 1: the battery cathode materials are classified according to the different kinds of metals in the materials. The synthesis methods, structural characteristics, capacity attenuation factors and existing problems of three kinds of materials (LiNi0.5Mn1.5O4,LiMn2O4 and LiNiO2) are mainly introduced in this paper. The modification studies of doping and physical mixing were summarized. Chapter 2: spinel LiNi0.5Mn1.5O4, was synthesized by secondary drying coprecipitation method and modified by sol-gel method. The cathode material with uniform LiCoPO4 coating on LiNi0.5Mn1.5O4 surface was prepared. The concept of the active battery material which is close to the bulk material is proposed. The material is characterized by means of XRD,SEM,TEM, AC impedance measurement. The experimental results show that the material can be used as the coating material. The existence of 2wt%LiCoPO4 coating obviously improves the electrochemical performance and thermal stability of the battery materials. Chapter 3: on the basis of the experimental contents in the previous chapter, we change the coating method, coating Co3 (PO4) 2 on the surface of the precursor, then mix it with LiOH H2O, and then prepare the LiNi0.5Mn1.5O4, coated with LiCoPO4 by one step sintering. The results of transmission electron microscope (TEM) showed the existence of the coating layer, while the blue electric test showed that the properties of the coating were improved after the coating modification. In chapter 4, the mixed electrode was prepared by sol-gel method with layered LiNiO2 and spinel LiMn2O4, at 1:9 mass ratio. The successful preparation of the battery material was proved by means of XRD, and the electrochemical properties of the mixed electrode and single electrode were tested respectively. The results show that the mixed electrode has higher discharge capacity, better rate performance and better cycle stability than the single LiMn2O4 electrode.
【学位授予单位】：河南师范大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912;TQ131.11

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