水热法制备磷酸铁锂及掺杂改性研究

发布时间：2019-01-10 14:58

【摘要】：随着人类文明的不断进步和全球社会的经济发展，人类对各类新能源的需求与消耗与日俱增，而新能源的储藏、转移和利用，都需要以高性能的储能设备作为支撑。锂离子电池作为新一代储能设备，以其工作电压高、自放电小、无记忆效应、环保等优点成为移动电源的首选。磷酸铁锂作为最有前途的锂离子电池正极材料之一，具有价格低廉、容量高、寿命长、热稳定性好等诸多优点。但是，，LiFePO4的电子电导率和锂离子扩散速率很低，导致其实际比容量不高且高倍率性能很差，极大地限制了该电极材料在动力电池领域的大规模应用。目前，提高该材料电化学性能的改性方法主要有三种：减小颗粒尺寸，晶体掺杂和表面修饰。本论文采用水热合成法制备了LiFePO4/C材料，并通过离子掺杂对晶体进行改性。 首先，利用正交试验法研究了Ni2+、Mn2+掺杂实验中掺杂浓度、水热反应温度和水热反应时间对LiFePO4/C电化学性能的影响。结果表明，以0.1C充放电倍率下材料的性能为试验指标时，镍掺杂浓度对材料性能影响最大，在最佳合成工艺条件下合成的材料，首次放电比容量为150.9mAh g-1；锰掺杂正交试验中，试验各因素主要影响了材料的高倍率性能，其中水热反应温度影响最大，在最优合成工艺下，材料的10C充放电倍率下比容量为127mAh g-1。 其次，研究了镍掺杂改性磷酸铁锂的过程中，水热反应温度对于掺杂过程和材料性能的影响。通过ICP、FTIR等方法研究发现，水热反应温度影响了掺杂离子镍在产品晶格中的含量，同时影响了掺杂后晶格内的错位情况。当水热反应温度高于210℃时，镍掺杂能对材料起到积极的改性作用；水热反应温度为240℃时，材料具有最优异的电化学性能：20C充放电倍率下比容量为98.5mAh g-1，且循环性能也得到一定的改善。 最后，进一步考察了高价态的掺杂离子如Al3+和Ti4+对磷酸铁锂掺杂改性过程中温度的影响。结果显示，高价态的离子在水热环境中由于水解作用，影响了水热反应中晶体的生长环境，进而对材料的纯度、产品的形貌和尺寸产生影响，而随着反应温度的升高，这一影响逐渐减弱。然而，Al3+和Ti4+掺杂后材料的电化学性能并未得到改善。
[Abstract]:With the progress of human civilization and the economic development of global society, the demand and consumption of all kinds of new energy are increasing day by day, and the storage, transfer and utilization of new energy need to be supported by high-performance energy storage equipment. As a new generation of energy storage equipment, lithium ion battery has become the first choice of mobile power supply because of its high working voltage, small self-discharge, no memory effect, environmental protection and so on. As one of the most promising cathode materials for lithium ion batteries, lithium iron phosphate has many advantages, such as low price, high capacity, long life, good thermal stability and so on. However, the electronic conductivity and lithium ion diffusion rate of LiFePO4 are very low, which leads to its low specific capacity and poor performance of high rate, which greatly limits the large-scale application of the electrode material in the field of power battery. At present, there are three main ways to improve the electrochemical properties of the material: reduction of particle size, crystal doping and surface modification. In this paper, LiFePO4/C materials were prepared by hydrothermal synthesis, and the crystals were modified by ion doping. Firstly, the effects of doping concentration, hydrothermal reaction temperature and hydrothermal reaction time on the electrochemical properties of Ni2 and Mn2 were studied by orthogonal test. The results show that the nickel doping concentration has the greatest influence on the properties of the material when the performance of the material under 0.1 C charge-discharge ratio is taken as the test index, and the first discharge specific capacity of the material synthesized under the optimum synthetic conditions is 150.9mAh g-1. In the manganese-doped orthogonal experiment, the experimental factors mainly affect the high rate performance of the material, and the hydrothermal reaction temperature has the greatest influence on the material. Under the optimum synthesis process, the specific capacity of the material is 127mAh g-1 at the charge / discharge rate of 10C. Secondly, the effect of hydrothermal reaction temperature on the doping process and properties of nickel doped lithium ferric phosphate was studied. By means of ICP,FTIR and other methods, it is found that the hydrothermal reaction temperature affects the content of doped nickel in the product lattice and the dislocation in the doped crystal lattice. When the hydrothermal reaction temperature is higher than 210 鈩

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