采用热解浮选回收废旧锂离子电池中磷酸铁锂

Recovery of LiFePO_(4) from spent lithium-ion batteries by pyrolysis flotation

随着全球磷酸铁锂电池退役量的增加,废旧磷酸铁锂电池电极材料的高效分离与回收利用技术亟待突破。本研究采用热解工艺去除废旧锂离子电池中磷酸铁锂颗粒表面的有机黏结剂,通过改变其表面润湿性,以实现正负极颗粒的高效浮选分离。借助XRD、XPS、SEM-EDS、TEM等手段,系统研究热解对电极材料表面元素含量、化学态变化、形貌、物相和粒径的影响,揭示热解对电极材料表面改性的机理。结果表明:随着热解温度的升高,磷酸铁锂暴露出大量亲水性表面;随着热解时间的延长,磷酸铁锂的亲水性先增加后降低。当热解温度为500℃时,聚偏氟乙烯(PVDF)中的—(CH_(2)CF_(2))_(n)—完全断裂,热解产物单分子氟化物继续分解,留下热解碳。磷酸铁锂物相和粒径在热解过程中基本保持不变。对最佳热解条件下(600℃、30 min)得到的热解产物进行浮选分离,精矿中磷酸铁锂品位为87.88%,回收率为95.17%。以回收的磷酸铁锂精矿作为正极材料制备电池,其在0.2C充放电倍率下的放电比容量为133.65 mA·h/g。

With the increase of lithium iron phosphate battery retirement in the world,the technology of efficient separation and recycling of waste lithium iron phosphate battery electrode materials needs to be broken through.In this study,the pyrolysis process was used to remove the organic binder on the surface of lithium iron phosphate particles in waste lithium ion batteries,and the surface wettability was changed to achieve efficient flotation separation of positive and negative electrode particles.By means of XRD,XPS,SEM-EDS,TEM and other advanced analysis and testing methods,the effects of pyrolysis on the surface element content,chemical state change,morphology,phase and particle size of electrode materials were systematically studied,and the mechanism of surface modification of electrode materials by pyrolysis was revealed.The results show that with the increase of pyrolysis temperature,lithium iron phosphate exposes a large number of hydrophilic surfaces.With the increase of pyrolysis time,the hydrophilicity of lithium iron phosphate increases first and then decreases.At 500 ℃,—(CH_(2)CF_(2))_n—in polyvinylidene fluoride( PVDF) is completely broken,and the pyrolysis product monomolecular fluoride continues to decompose,leaving pyrolytic carbon.The phase and particle size of lithium iron phosphate remained basically unchange during pyrolysis.Flotation was carried out on the pyrolysis products obtained under the optimum pyrolysis conditions of 600 ℃ and 30 min.The grade of lithium iron phosphate in the concentrate is 87.88 % and the recovery rate is 95.17 %.The recycled lithium iron phosphate concentrate is used as the cathode material to prepare the battery,and its discharge specific capacity is 133.65 mA·h/g at 0.2C charge and discharge rate.