| 磷酸铁锂废料中FePO4·2H2O提取及其杂质形成机理 |
| Recycling FePO4·2H2O from waste LiFePO4 powders and formation mechanisms of the impurities during precipitation process |
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| 摘要: 采用化学共沉淀方法从磷酸铁锂废料中提取FePO4·2H2O，并研究了回收过程中杂质形成的机理。在热力学计算基础上绘制了298和363 K时Fe-P-Li-H2O体系的电势（φ）-pH图，结果表明当pH≤5.0时，Fe（OH）3相可以自发地转成FePO4·2H2O相，从而得到高纯的FePO4·2H2O。但实验结果发现当溶液中铁、磷的物质的量之比（nFe∶nP）为1∶1，合成pH为1.5~2.2时得到的FePO4·2H2O中存在Fe（OH）3杂质，这是因为在共沉淀过程中少量Fe3+以Fe（OH）3快速沉淀，而陈化时Fe（OH）3相转化速率慢，因此FePO4·2H2O中含有Fe（OH）3杂相，而在后续的煅烧过程中Fe（OH）3会与FePO4·2H2O进一步反应生成Fe3PO7。FePO4·2H2O中Fe（OH）3的含量随合成的pH值和温度升高而快速增加。而nFe∶nP=1∶2时，溶液中部分H3PO4与NaOH反应生成NaH2PO4，煅烧时NaH2PO4与FePO4·2H2O反应生成NaFeP2O7杂相，进一步降低磷酸铁的纯度。当溶液中nFe∶nP=1∶1，共沉淀温度为333 K，反应终点pH值为1.5时，可以制备出纯度为99.97% 的FePO4·2H2O。用此FePO4·2H2O合成的LiFePO4正极材料，其放电比容量为154.1 mAh·g-1，以0.2C（1C=180 mA·g-1）充放电循环100周后容量保持率为96.79%，具有优异的电化学性能，可用于制备磷酸铁锂电池。 |
| 关键词: 锂离子电池 废旧磷酸铁锂电池 共沉淀 LiFePO4 回收 |
| 基金项目: 季华实验室基金（No.X200191TL200，X220161XS220）资助 |
| Abstract: Applying waste LiFePO4 powders as raw material, the FePO4·2H2O precursor was effectively recycled through chemical precipitation. Thereafter, the formation mechanisms of the impurities were discussed. The potential (φ)-pH diagram of the Fe-P-Li-H2O system was investigated and the result demonstrated that FePO4·2H2O could form at a temperature of 298-363 K under a pH value of 0-5.0 by precipitation. The experiment results indicated that the Fe3PO7 phase started to form through the reaction of Fe(OH)3 and FePO4·2H2O during the sintering process. When the molar ratio of Fe and P (nFe:nP) was 1:1, pH=1.5-2.2, some Fe3+ ions will form Fe(OH)3, and the yield coefficient increased with the pH and temperature. This is because the solubility product constant (Ksp) of Fe(OH)3 was much less than the one of FePO4·2H2O, suggesting that the precipitate rate of Fe(OH)3 was faster than FePO4·2H2O. Based on thermodynamic principles, aging may be an effective way to convert Fe(OH)3 into FePO4 ·2H2O according to the φ-pH diagram of the Fe-P-Li-H2O system. Unfortunately, the rate of Fe(OH)3 conversion was slowed, resulting in some Fe(OH)3 in precipitation. Therefore, low pH value and temperature are essential to avoid Fe(OH)3 generation during the co-precipitation process. Also, when nFe:nP=1:2, some H3PO4 could react with NaOH to form NaH2PO4, which would further react with FePO4·2H2O to produce NaFeP2O7 during the sintering process. At 333 K, the equimolar ratio of co-precipitation precursor FePO4·2H2O can be obtained by adjusting the pH value at 1.5, matching the molar ratio of 1:1 of Fe to P. The purity of this as-prepared FePO4·2H2O was 99.97%. Besides, the synthesized LiFePO4 which used this FePO4·2H2O as a precursor exhibited a reversible capacity of 154.1 mAh·g-1 and excellent capacity retention of 96.79% after 100 cycles at 0.2C (1C=180 mA·g-1). FePO4·2H2O obtained from waste LiFePO4 powders can be used as precursor to synthesize LiFePO4 cathode material, which greatly improves the economic effi-ciency of recycling the spent LiFePO4 battery. |
| Keywords: lithiumion battery spent lithium iron phosphate battery co-precipitation LiFePO4 recycle |
| 投稿时间：2022-09-09 修订日期：2022-11-18 |
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| 黄玲,张成智,谭军,李穗敏.磷酸铁锂废料中FePO4·2H2O提取及其杂质形成机理[J].无机化学学报,2023,39(2):357-366. |
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