基于微纳米尺寸的铁氧体热磁学性能研究及其形貌结构应用于锂电池负极材料的影响

发布时间：2018-05-04 20:17

本文选题：氧化铁 + 纳米颗粒　；参考：《宁波大学》2017年硕士论文

【摘要】：近年来,随着纳米器件尺寸的不断减小,纳米材料的尺寸效应、相稳定性等性质研究逐渐成为研究讨论的热点。而铁氧体作为纳米材料中重要的研究对象,更是因为其广泛的实际应用,具有更高的研究价值。本论文中,通过制备从纳米至微米级别一系列不同尺寸下的α-Fe_2O_3纳米结构作为研究对象,利用综合物性测量系统对样品的热学性能、磁学性能进行了较为系统的研究。除此之外,也对α-Fe_2O_3纳米材料的结构形貌对应用于锂离子电池负极材料上的影响作了详实的研究。本文的主要研究成果如下:(1)我们通过水热法合成了一系列尺寸的单晶α-Fe_2O_3纳米立方块体。在高真空(9.5×10-6 Torr)下通过920K之前的磁学性能的测量表明,单晶纳米颗粒随着其尺寸的减小,其热稳定性逐渐降低,对应的相转变点由~850nm的729K转变温度减小到~40nm的609K转变温度。而且,我们通过引入焓值的理论来有效地支持并解释这一实验结果。(2)我们测量了该系列α-Fe_2O_3纳米结构在上述相转变点前后的磁学性能。实验结果发现,对于α-Fe_2O_3纳米立方块体,随着尺寸的减小,其矫顽力、剩磁值都逐渐降低,整条磁化曲线呈缩小趋势,即表明更小的纳米尺寸可以在反复磁化/去磁过程中有效地减小能量损失。而对于相变后的铁氧体纳米颗粒,其饱和磁化强度随着样品尺寸的减小而显著增大,并且我们通过进一步的RIR算法,半定量的计算出相变过程中的转变量。另外,我们对纳米尺寸下的样品,测量了其不同尺寸的Morin转变温度的影响,进一步支持了前人的结论。(3)我们以铁氧体作为本次的研究对象,通过调节实验参数,有效的调控合成了一系列直径在~100nm左右,长度由100nm~`600nm的空心环结构样品。结果发现,随着样品结构尺寸的缩小,其首次充放电容量会呈现逐渐增大的趋势。对于100nm尺寸的样品,0.1倍率下可达到1200 m A h g~(-1);而随着尺寸的增加,同样倍率下其首次放电容量降至约800m A h g~(-1)。在充放电循环稳定性方面,其性能的表现却并未和结构尺寸大小呈单调性关系。对于这一结果,我们理解为随着样品尺寸的减小,其比表面积增大,促使电极材料与电解液具有更好的接触,从而增强了Li~+的迁移率;但与此同时,更大的电极材料与电解液接触面会导致Li~+在充放电循环的镶嵌/脱嵌过程中有效利用率降低,从而导致随着充放电循环的持续,性能衰退更为严重,循环稳定性变差。
[Abstract]:In recent years, with the continuous reduction of the size of nano-devices, the size effect, phase stability and other properties of nanomaterials have gradually become the focus of discussion. Ferrite is an important research object in nanomaterials, because of its extensive practical application, it has higher research value. In this thesis, a series of 伪 -Fe _ 2O _ 3 nanostructures with different sizes from nanometer to micron were prepared as the research object. The thermal and magnetic properties of the samples were systematically studied by using a comprehensive physical property measurement system. In addition, the effects of the structure and morphology of 伪 -Fe2O3 nanomaterials on the negative electrode materials for lithium ion batteries are also studied in detail. The main results of this paper are as follows: (1) A series of single crystal 伪 -Fe _ 2O _ 3 nanocrystalline cubic blocks have been synthesized by hydrothermal method. The measurement of the magnetic properties before 920K under high vacuum condition (9.5 脳 10-6 Torr) shows that the thermal stability of the monocrystalline nanoparticles decreases with the decrease of their size, and the corresponding phase transition temperature decreases from 729K at 850nm to 609K at 40nm. Furthermore, the enthalpy theory is introduced to effectively support and explain the experimental results.) We have measured the magnetic properties of the 伪 -Fe2O3 nanostructures before and after the phase transition point. The experimental results show that the coercivity and remanent magnetic value of the 伪 -Fe2O3 nanocube gradually decrease with the decrease of the size, and the whole magnetization curve tends to decrease. It is shown that the smaller nanometer size can effectively reduce the energy loss in the process of repeated magnetization / demagnetization. For the ferrite nanoparticles after phase transition, the saturation magnetization increases significantly with the decrease of the sample size, and we use further RIR algorithm to semi-quantitatively calculate the transition amount in the phase transition process. In addition, we have measured the effect of Morin transition temperature of different sizes on the samples with nanometer size, which further supports the previous conclusion. (3) We take ferrite as the object of this study, and we adjust the experimental parameters by adjusting the experimental parameters. A series of hollow ring structures with diameter of about 100nm and length of 100nm ~ '600nm were synthesized. The results show that the first charge and discharge capacity of the sample increases gradually with the decrease of the size of the sample structure. For the sample of 100nm size, the initial discharge capacity decreases to about 800mAh / g ~ (-1) with the increase of the size of the sample at 1200 m A h / g ~ (-1) ratio, and the initial discharge capacity decreases to about 800mA / g ~ (-1) with the increase of the size of the sample. In terms of the stability of charge-discharge cycle, the performance of the performance is not monotonic to the size of the structure. For this result, we understand that with the decrease of sample size, the specific surface area increases, which leads to better contact between electrode material and electrolyte, which enhances the mobility of Li-3, but at the same time, The larger interface between electrode material and electrolyte will lead to the decrease of the effective utilization ratio of Li ~ in the inlay / descalation process of charge / discharge cycle, which leads to the deterioration of the performance and the deterioration of the cycle stability as the charge / discharge cycle continues.
【学位授予单位】：宁波大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1;O614.811

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