Knowledge Management System Of Institute of process engineering,CAS
磷酸铁锂电池是我国新能源汽车产业发展初期的主流动力电池，具有安全性能好、循环寿命长、成本低等突出优点，一直是电动商用车、专用车和储能领域的首选电源，目前面临退役量爆发式增长、亟待回收处理的迫切需求。磷酸铁锂正极材料是磷酸铁锂电池价值最高的部件，仅含少量的锂及廉价的铁/磷，总体价值较低，目前尚无经济、有效的回收利用技术。本论文以废磷酸铁锂正极粉铁磷组分高值回收为目标，提出废磷酸铁锂正极粉磷酸法制备磷酸铁技术路线，重点开展了废正极粉磷酸浸出、浸出液络合除铝、磷酸铁沉淀等过程的应用基础和工艺优化研究。主要研究结果如下：（1）以含铝的废磷酸铁锂正极粉为原料，系统研究了酸料比、浸出温度等主要参数对废磷酸铁锂正极粉浸出过程的影响规律，考察了浸出过程宏观动力学。研究结果表明，酸料比、液固比对磷酸铁锂和铝的浸出率影响最为显著，采用阴离子型表面活性剂SDS（十二烷基硫酸钠）可有效解决废正极粉浸出过程亲水性差的难题。在酸料比1.1:1、温度20 ℃、液固比5:1、搅拌速度400 rpm、浸出时间120 min的优化条件下，磷酸铁锂浸出率大于93%，铝浸出率小于20%。废磷酸铁锂正极粉磷酸浸出过程符合无固态产物层的收缩核模型，表观活化能为24.62 kJ/mol，浸出过程受扩散控制，浸出过程动力学方程为：（2）提出了废磷酸铁锂正极粉磷酸浸出液中氟化物络合除铝新方法，重点研究了以氟化钠和氢氟酸为除铝剂时，各主要工艺参数对浸出液中铝脱除效果的影响规律。通过理论计算，获得以氟化钠为除铝剂时溶液氢离子浓度和总氟浓度对除铝效果的关系式，其中总氟浓度影响更为显著，正交实验结果证实了理论分析结果；以氟化钠为除铝剂时，在反应温度50 ℃，溶液初始pH为1.8、氟化钠加入量为铝的6倍（物质的量之比）、反应30分钟的优化条件下，除铝率可达97%以上，浸出液中铝浓度可降低到48 ppm，除铝产物为六氟铝酸钠；以氢氟酸为除铝剂时，在反应温度30 ℃、溶液初始pH为2，氢氟酸加入量为铝的6倍（物质的量之比）、反应20分钟的优化条件下，除铝效率可达95%以上，除铝产物为六氟铝酸锂。（3）提出并建立了铁磷溶液在弱酸（pH<2）下磷酸铁直接沉淀新方法，研究了主要工艺参数对磷酸铁沉淀过程的影响规律，并考察了铝、铜、钠三种阳离子杂质对磷酸铁产品成分的影响。研究结果表明，溶液酸度、沉淀温度对磷酸铁沉淀率影响显著，溶液初始铁浓度和晶种对沉淀率影响不大，在溶液pH值>0.7，沉淀温度95 ℃，初始铁浓度<35 g/L的优化条件下，磷酸铁沉淀率大于88%；磷酸铁中铝、铜含量与沉淀前液中的铝、铜含量呈直接关系，而磷酸铁中钠含量需使用大量水洗涤脱除。（4）提出废磷酸铁锂正极粉磷酸法制备二水磷酸铁原则流程，包括废正极粉磷酸浸出、除铝、氧化、沉淀等多个步骤，并用实际含铝的废磷酸铁锂正极粉进行了全流程验证实验，可获得Al、Fe、P成分合格的二水磷酸铁产品。 ;Lithium iron phosphate (LiFePO4, briefed as LFP) battery is the mainstream power battery in the early development of China's new energy automobile industry. It has always been the preferred power battery for electric commercial vehicles, special vehicles and energy storage due to its outstanding advantages such as good safety performance, long cycle life and low cost. The explosive growth of retired LFP batteries demands the urgent need for recycling. Lithium iron phosphate cathode material is the most valuable component of lithium iron phosphate batteries, but the value for recycling is still low because it contains only a small amount of lithium and cheap iron/phosphorus. Currently, there is no economical and effective recycling technology.This paper focuses on the utilization of iron and phosphorus resources in the spent lithium iron phosphate cathode powder. A new process for preparing iron phosphate from spent lithium iron phosphate cathode powder by phosphoric acid method was proposed in the paper. The paper focused on the fundamental and process optimization research of acid leaching of spent cathode powder phosphoric, removing aluminum from the leaching liquor by complexing method, and the precipitation of iron phosphate. The main findings are as follows:(1) Effects of main process parameters such as acid-to-material ratio, leaching temperature on the leaching process of spent LFP cathode powder was systematically studied by using aluminum-containing spent lithium iron phosphate cathode powder as raw material, and the macro-dynamics of the leaching process was also investigated. The research results show that the acid-to-material ratio and liquid-solid ratio have the most significant impact on the leaching rate of lithium iron phosphate and aluminum. The use of anionic surfactant SDS (sodium dodecyl sulfate) can effectively solve the problem of poor hydrophilicity of the spent cathode powder in leaching process. Under the optimized conditions of acid-to-material ratio of 1.1, temperature of 20 ℃, liquid-to-solid ratio of 5:1, stirring speed of 400 rpm, and leaching time of 120 min, the leaching rate of lithium iron phosphate is greater than 93%, and the leaching rate of aluminum is less than 20%. The phosphoric acid leaching process of spent lithium iron phosphate cathode powder conforms to the shrinking core model without solid product layer, and the apparent activation energy is 24.62 kJ/mol. The leaching process is controlled by diffusion, and the kinetic equation of the leaching process is as follows:(2) A new method for removing aluminum by complexation of fluoride in phosphoric acid leaching solution of spent cathode powder is proposed. Effects of the main process parameters on the removal efficiency of aluminum in the leaching solution when sodium fluoride and hydrofluoric acid are used as aluminum removal agents. By theoretical calculation, the relationship between the hydrogen ion concentration and total fluorine concentration of the solution on the aluminum removal effect when sodium fluoride is used as the aluminum removal agent is obtained. It was found that the total fluorine concentration has a more significant effect on the aluminum removal effect than the acidity, which was verified by the orthogonal experiment results. When sodium fluoride is used as the aluminum removal agent, under the optimized condition of the reaction temperature 50 ℃, the initial pH of the solution 1.8, 6 times the molar amount of sodium fluoride added that of aluminum, and the reaction time 30 minutes, the aluminum removal efficiency can reach more than 97%, and the aluminum concentration in the leaching solution can be reduced to 48 ppm with sodium hexafluoroaluminate as the aluminum removal product. When hydrofluoric acid is used as the aluminum removal agent, under the optimized condition of the reaction temperature 30 ℃, the initial pH of the solution 2, 6 times the molar amount of sodium fluoride added that of aluminum, and the reaction time 20 minutes, the aluminum removal efficiency can reach more than 95%, and the aluminum removal product is lithium hexafluoroaluminate.(3) A new method for direct precipitation of iron phosphate from iron-phosphorus solution under weak acid (pH<2) was proposed. Effects of main process parameters on the precipitation process of iron phosphate was studied, and the influence of impurity cations such as aluminum, copper and sodium on the composition of iron phosphate products was investigated. The research results show that the acidity of the solution as well as the precipitation temperature have significant effects on the precipitation rate of iron phosphate, and the initial iron concentration and seed crystals of the solution have little effect on the precipitation rate. Under optimized conditions of the pH value higher than 0.7, the precipitation temperature 95 ℃ and the initial iron concentration less than 35 g/L, the precipitation efficiency of iron phosphate is more than 88%. The content of aluminum and copper in iron phosphate is directly related to the content of aluminum and copper in the pregnant solution, while the sodium content in iron phosphate needs to be removed by washing with a large amount of water.(4) The principle process of preparing iron phosphate dihydrate from spent lithium iron phosphate cathode powder by phosphoric acid method was proposed in the paper, including multiple procedures of phosphoric acid leaching, aluminum removing, oxidation of ferrous, and precipitation of iron phosphate. The whole process has been experimental verified by using real aluminum-containing spent lithium iron phosphate cathode powder, and ferric phosphate dihydrate products with qualified Al, Fe and P components can be obtained.
|万青珂. 废磷酸铁锂正极粉磷酸法制备磷酸铁工艺研究[D]. 中国科学院大学,2020.|
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