P2相Na2/3Ni1/6Co1/6Mn2/3O2钠离子电池正极材料的制备与电化学性能研究

SYNTHESIS AND ELECTROCHEMICAL PERFORMANCE OF P2 Na2/3Ni1/6Co1/6Mn2/3O2 CATHODE MATERIAL FOR SODIUM ION BATTERY

唐雅欣

11849141

硕士

材料工程领域工程

邓永红

2020-05-30

2020-07-20

哈尔滨工业大学

深圳

钠离子电池作为一种二次可逆充放电电池，具有丰富的原料资源以及相对稳定的电化学性能，被认为是最具有潜力的候选储能系统之一。但目前钠离子电池的能量密度、倍率性能和循环稳定性仍受正极材料的限制。基于过渡金属离子与晶格氧双重氧化还原反应的层状过渡金属氧化物正极材料具有较高的比容量，是实现高比能量钠离子电池较为理想的正极材料。然而，由于钠离子的离子半径较大导致其扩散缓慢，因此钠离子电池正极材料的发展仍然面临着巨大的挑战。本文通过共沉淀法制备了P2相过渡金属层状氧化物Na2/3Ni1/6Co1/6Mn2/3O2，并以其为研究对象，对其电化学性能、高压下相转变对材料的影响以及不同添加剂对于该材料与硬碳组装的全电池性能影响进行了一系列研究。本文借助X射线衍射（XRD）、扫描电子显微镜（SEM）表征方式研究了Co掺杂对材料结构和电化学性能的影响规律。研究表明：1）通过Co元素的掺杂使得材料晶体结构的晶胞参数c/a变大，倍率性能得到了提升，在20C（1C=100 mA/g）的倍率下仍然有38 mAh/g的容量，同时通过GITT测试和计算发现材料的钠离子扩散系数得到了提升；2）材料具有良好的循环性能，在100 mA/g的电流密度下循环800圈容量保持率为73%。此外，本文对材料不同截止电压下的电化学性能进行了探究，发现材料在高压条件下材料容量衰减迅速。通过原位XRD探究得出该过渡金属层状氧化物正极材料在高压条件下会发生不可逆的相变，从而导致性能衰减。利用透射电子显微镜（TEM）观测材料在相变后产生的微观裂纹的分布以及深度，并通过对微观裂纹的研究进一步阐述了该类材料在循环充电过程中高电压下的容量衰减机理，发现在高压下的重复相变导致晶格中残余应力存在，使得材料出现晶内裂纹是导致材料容量衰减的主要原因。为了使此研究对于钠离子电池在实际工业生产中具有参考价值以及指导作用，研究电解液与正负极材料的适配也具有重要意义。本文利用Na2/3Ni1/6Co1/6Mn2/3O2作为正极材料，硬碳为负极材料，组装了全电池。通过改变电解液添加剂组分，如氟代乙烯酯 (FEC)、1,3-丙烷磺内酯（PS）以及PS/FEC，探究不同添加剂对于全电池的电化学性能影响。并最终发现在添加剂FEC与PS两者共同存在时，钠离子全电池器件具有较高的能量密度、大倍率性能以及良好的循环稳定性（在100圈循环后仍可保持79%的容量）。

As a secondary battery, sodium ion battery has wide raw material resources and relatively stable electrochemical performance, and is considered as one of the most promising energy storage systems. However, due to the large ionic radius of sodium ions and their slow diffusion, the development of cathode materials for sodium ion batteries still faces huge challenges. In this paper, P2-type Na2/3Ni1/6Co1/6Mn2/3O2 has been prepared by a co-precipitation method for sodium ion batteries. Taking it as the research object, a series of studies were conducted on its electrochemical performance, the effect of phase transformation on the material under high voltage, and the effect of different additives on the performance of the full cell assembled with the hard carbon.In this paper, the structure and morphology of the material have been characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. Through the introduction of Co element, the material's rate capability has been improved, and it delivers a specific discharge capacity of 38 mAh/g at a rate of 20 C (1C = 100 mA/g). Through the GITT test and calculation, it is found that the sodium ion diffusion coefficient of the material has been improved. In addition, the material also exhibits good cycling performance, and the capacity retention rate after 800 cycles at 1C is 73%.In addition, the electrochemical performance of P2-type Na2/3Ni1/6Co1/6Mn2/3O2 under different cut-off voltages is explored, and it is found that the material capacity decays rapidly under high-voltages. To explore the mechanisms, in-situ XRD and transmission electron microscope (TEM) characterizations have been performed. Through in-situ XRD investigation, it is concluded that the transition metal layered oxide cathode material will undergo an irreversible phase change under high voltages. The TEM was used to observe the distribution and depth of the micro-cracks generated after the phase transition of the material, and the micro-cracks were further elaborated to explain the capacity decay mechanism of such materials under high voltage during the cyclic charging process. The repetitive phase transitions in the following lead to the existence of residual stresses in the crystal lattice, and the occurrence of intracrystalline cracks in the material is the main reason for the attenuation of the material capacity.In order to make this research have a reference value and a guiding role for sodium ion batteries in actual industrial production, it is also of great significance to study the adaptation of the electrolyte to the positive and negative electrode materials. In this paper, Na2/3Ni1/6Co1/6Mn2/3O2 is used as the positive electrode material, and hard carbon is used as the negative electrode material to assemble the full battery. By changing the electrolyte additive components, such as fluorinated vinyl ester (FEC), 1,3-propane sultone (PS) and PS / FEC, to explore the impact of different additives on the electrochemical performance of the whole battery. And finally found that when both the additives FEC and PS coexist, the sodium ion full-cell device has higher energy density, large rate performance and good cycle stability (79% capacity can be maintained after 100 cycles).

钠离子电池 正极 层状过渡金属氧化物

sodium ion batteries cathode material layered transition metal oxide

中文

联合培养

南方科技大学

唐雅欣. P2相Na2/3Ni1/6Co1/6Mn2/3O2钠离子电池正极材料的制备与电化学性能研究[D]. 深圳. 哈尔滨工业大学,2020.