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2021年,我国新能源汽车年销售量达352.1×104辆,同比增长1.6倍[1]。锂电池作为新能源汽车的重要组成部分,具有高电压、高比容量、循环寿命长、对环境无污染等诸多优势,成为电源装置中的主导产品[2]。而具有更好的电化学性能、温度稳定性、安全性和循环寿命的磷酸铁锂正极材料的出现[3],更是促进了锂电池和新能源汽车的发展。磷酸铁锂电池在电动船舶、商用车、通讯基站等领域亦具有广阔的应用前景[4-8]。
磷酸铁锂电池经过一定的循环次数,在达到8~10年的使用期限后将会报废,预计到2025年,报废磷酸铁锂动力电池将近100×104 t[9-10],而电池的随意丢弃会污染土壤,导致环境酸碱度增高;同时会造成锂资源的浪费,不符合低碳循环的绿色发展理念。为保障“无废城市”建设的稳步推进,降低固体废物产生的强度,提升固体废物的综合利用水平,打好污染防治攻坚战,对废旧磷酸铁锂电池正极材料的资源化回收利用是势在必行的。
目前,对于废旧磷酸铁锂电池的回收主要是直接物理再生和湿法冶金2种途径[11]。SUN等[12]设计了一条绿色全固态路线,将经过纯化和均质化预处理后的废料与不同量的Li2CO3和20% (质量浓度) 蔗糖混合,在惰性氛围下,350 ℃加热5 h,然后在650 ℃加热10 h重新合成LiFePO4/C材料,在半电池和全电池测试中表现出优异的物理、化学和电化学性能。LIANG等[13]通过添加相应的Li、Fe、P盐后进行球磨和喷雾干燥,在氮气气氛下,650 ℃热处理10 h得到灰白色修复的LiFePO4粉末,修复后的LiFePO4材料的容量高达139 mAh·g−1。直接物理再生不涉及酸碱的使用,避免了二次废液的产生,但是高温煅烧带来的高能耗并不符合绿色化工的理念。湿法冶金主要是将经过预处理后的废旧LiFePO4/C粉末以离子形式浸出到溶液中,经过浓缩、提纯后生成金属盐或其他产物[14]。按照浸出方式的不同可分为无机酸浸法、有机酸浸法、氧化性无机盐浸出法和非氧化性无机盐浸出法[15]。KUMAR等[16]利用100%的柠檬酸作为浸出剂进行浸出实验,Li的浸出率最高达94.83%,Fe、P元素以FePO4形式回收再生LiFePO4/C材料,该实验柠檬酸廉价且易降解,对环境友好,但浸出过程中Fe的损失率达4.05%。ZHANG等[17]用理论量的1.05倍Na2S2O8氧化LiFePO4至FePO4,从废旧LiFePO4电池中选择性回收锂,Li的浸出率最高达99.9%,该方法减少了酸碱的使用,且Li的浸出效率高,但会引入大量Na2SO4。HUANG等[18]用HCl+H2O2浸出废旧LiFePO4 / LiMn2O4混合正极电池材料,固液分离得到含有Fe3+、Mn2+和Li+等离子的浸出液,回收效率高,产品纯度高,但HCl容易挥发而产生毒性。因此,本研究主要选取沸点比较高的H2SO4作为浸出溶剂,同时使用对环境友好的H2O2作为氧化剂,整个浸出工艺符合废旧磷酸铁锂电池电极材料绿色回收的发展趋势。
本研究采用湿法工艺,研究了浸出时间、浸出温度、pH、L/S以及H2O2/Li的摩尔比对废旧磷酸铁锂正极材料中3种离子 (Li、Fe、P) 浸出率的影响,通过浸出液的二次浸出实现了对Li的高效率浸出,并以棒状Li2CO3的形式回收;同时通过控制pH来减少Fe、P的浸出,并以FePO4/C形式进行回收。本研究结果可为选择性高效浸出废旧磷酸铁锂电池电极材料中锂的新工艺开发提供参考。
废旧磷酸铁锂电池正极材料浸出回收锂工艺
Leaching and recovering technology of lithium from the cathode material of waste lithium iron phosphate batteries
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摘要: 为实现对废旧磷酸铁锂电池的高效资源化回收,提出了一种双氧水氧化—酸浸—浸出液二次浸出的工艺回收正极材料中的Li。通过浸出液二次浸出,选择性地从LiFePO4/C中浸出Li,既减少了双氧水的用量,又提高了锂离子浸出率。通过扫描电子显微镜 (SEM) 、原子吸收光谱仪 (AAS) 、X-粉末衍射仪 (XRD) 等分析表征手段考察了浸出温度、浸出时间、液固比 (L/S) 、pH以及H2O2/Li的摩尔比对Li、Fe、P元素浸出率的影响。结果表明,通过浸出液的二次浸出,Li的浸出率从94.82%上升到99.46%;同时,Fe和P的浸出率分别控制在0.03%和2.3%之内,为后续Fe、P的回收创造了有利条件。所得的Li2SO4浸出滤液,经过进一步的除杂和沉锂后得到Li2CO3白色粉末;Fe、P以橄榄型无水FePO4的形式存在于灰色浸出渣中。本研究结果可为废旧磷酸铁锂电池正极材料中锂的工业化回收提供参考。Abstract: In order to achieve the efficient resource recovery of waste lithium iron phosphate batteries, this paper proposed a process of oxidation-acid leaching-secondary leaching of the filtrate via hydrogen peroxide to recycle Li from the cathode material. By selectively leaching of Li from LiFePO4/C in secondary leaching of the filtrate, the consumption amount of hydrogen peroxide reduced and the leaching rate of lithium ion was improved. The effects of leaching temperature, leaching time, liquid-solid ratio (L/S), pH and the molar ratio of H2O2/Li on the leaching rates of Li, Fe and P were investigated by scanning electron microscopy (SEM), atomic absorption spectroscopy (AAS), X-ray powder diffraction (XRD) and other analytical detection methods. The results showed that the leaching rate of Li increased from 94.82% to 99.46% through secondary leaching of the filtrate, and the leaching rates of Fe and P were controlled within 0.03% and 2.3%, respectively, further creating favorable conditions for the subsequent recycle of Fe and P. White powder of Li2CO3 was obtained via further impurity removal and lithium deposition of the resulting Li2SO4 filtrate; Fe and P were presented in the gray leaching slag with the form of olive-shaped anhydrous FePO4. This paper provides a reference for the industrial recycling of lithium from the cathode materials of waste lithium iron phosphate batteries.
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表 1 第一次浸出不同H2O2/Li的摩尔比下Li、Fe、P的浸出率
Table 1. The leaching rates of Li, Fe, P under the different molar ratios of H2O2/Li in the first leaching %
元素 不同H2O2/Li摩尔比 0.5 0.8 1 1.3 1.5 1.8 Li 90.69 93.78 92.86 93.87 94.82 94.46 Fe 0.007 0.008 0.009 0.011 0.011 0.016 P 1.59 1.72 1.76 1.85 1.56 1.83 表 2 废旧磷酸铁锂电池的不同浸出工艺参数的比较
Table 2. Comparison of different leaching process parameters of waste lithium iron phosphate batteries
浸出剂 氧化剂 浸出时间/min 浸出温度/ ℃ Li、Fe、P浸出率/% 文献 pH=3.66 H2SO4 2.2 vol% H2O2 120 60 96.85、0.027、1.95 [19] H2SO4/Li=0.56 Na2S2O8/Li=0.45 90 60 97.53、1.39、2.58 [20] HCOOH/Li=3.23 5 vol% H2O2 30 30 99.98、<0.50、<0.50 [21] pH=3.5 H2SO4 600 mL·min-1 空气 300 25 99.30、<0.02、<0.02 [9] H2SO4/Li=0.38 高温活化:600 ℃ 空气气氛 240 85 98.46、0.01、26.59 [22] pH≈3.5 100%柠檬酸 6 vol% H2O2 90 — 94.83、4.05、0.84 [16] pH=3.0 (H2SO4/Li=0.49) 2.2 vol% H2O2 120 50 99.46、0.029、2.25 本研究 -
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