水热法以磷铁制备电池级磷酸铁及改性研究

发布时间：2018-12-12 13:09

【摘要】：本文针对锂电池正极材料的研究热点及资源的循环利用,提出以黄磷副产物磷铁为原料,采用水热法将磷铁溶解与磷酸铁结晶一步完成的过程研究。本文方法实现了在水热条件下将磷铁的溶解与磷酸铁的结晶在相同体系中一步完成,研究了反应条件对产品磷酸铁纯度及电化学性能的影响。首先,以磷铁、H_3PO_4、HNO_3为原料采用水热法一步合成电池级磷酸铁,并利用XRD、TG-DSC、SEM、FTIR、ICP-Ms以及电化学测试等手段表征产品的分子结构、晶体结构、形貌和电化学性能。研究了水热反应过程中硝酸浓度、反应温度、反应时间及体系铁浓度对产品中铁含量及铁磷比的影响,设计正交试验优化实验条件,并对磷铁一步反应合成电池级磷酸铁的反应机理进行了初步的研究。其次,通过加入氢氟酸或超声处理对水热法制备的电池级磷酸铁进行改性研究,研究了氢氟酸浓度、浸泡时间、超声时间对磷酸铁纯度、结构、形貌及电化学性能的影响。实验结果表明:当硝酸浓度为3.0mol/L、反应温度为110℃、体系铁浓度为20g/L时反应120min后,通过分析表征可知产品在纯度、结构等方面都符合市售电池级磷酸铁的要求。同时以自制的FePO_4·2H_2O产品作为前驱体,采用高温固相法制备的LiFePO_4/C具有良好的电化学性能,电池在0.1C下的首次放电容量为148.9 mAh/g,且通过EIS测试显示电池电极电荷转移电阻为48Ω。这是由于磷酸铁产品中含有的钛、钒、锰等微量金属元素不仅有效利用了原料磷铁中的杂质金属元素,而且对电池起到了一定的掺杂作用,改善了磷酸铁锂的电化学性能。对磷酸铁的改性先采用浓度为4%的氢氟酸浸泡4h。并对氢氟酸处理前后磷酸铁产品的结构、形貌及电化学性能进行了分析对比。结果表明:氢氟酸处理后的产品在结构上没有发生改变,但产品形貌由团聚的层状结构分散为片状,并且在片状结构上存在许多不同大小的微孔,这在一定程度上增大了磷酸铁产品的比表面积。同时通过分析产品磷酸铁形貌及电池性能的变化可知,将氢氟酸处理与超声处理结合可有效缩短改性时间。
[Abstract]:Aiming at the research focus of cathode materials for lithium batteries and the recycling of resources, the process of dissolution of iron phosphate and crystallization of iron phosphate by hydrothermal method using yellow phosphorus by-product as raw material was put forward in this paper. In this paper, the dissolution of iron phosphate and the crystallization of iron phosphate in the same system were carried out in one step under hydrothermal conditions. The effects of reaction conditions on the purity and electrochemical properties of iron phosphate products were studied. First of all, the battery-grade ferric phosphate was synthesized by hydrothermal method using ferric phosphate, H3PO4 and HNOK3 as raw materials, and the molecular structure and crystal structure of the product were characterized by XRD,TG-DSC,SEM,FTIR,ICP-Ms and electrochemical tests. Morphology and electrochemical properties. The effects of nitric acid concentration, reaction temperature, reaction time and iron concentration of the system on the iron content and iron phosphorus ratio in the product during hydrothermal reaction were studied. The orthogonal test was designed to optimize the experimental conditions. The reaction mechanism of the one-step reaction of iron phosphate for the synthesis of battery-grade iron phosphate was studied. Secondly, the effects of hydrofluoric acid concentration, soaking time and ultrasonic time on the purity, structure, morphology and electrochemical properties of ferric phosphate prepared by hydrothermal method were studied by adding hydrofluoric acid or ultrasonic treatment. The experimental results show that when the concentration of nitric acid is 3.0 mol / L, the reaction temperature is 110 鈩，

本文编号：2374619