减压过滤除碳方式对碳包覆磷酸铁锂中铁含量测定结果的影响

碳的存在影响碳包覆磷酸铁锂(LiFePO₄/C)试样的溶解,采用减压过滤方式除碳有利于LiFePO₄/C试样中铁含量的测定。为确定该除碳方式对试样中铁含量测定结果有无影响,实验采用盐酸在160 ℃下溶解试样10 min、减压过滤除碳、重铬酸钾氧化和三氯化钛还原滴定法测定材料中的Fe含量。采用X射线衍射光谱(XRD)表征,发现滤渣碳与无定形碳的XRD图谱极为相似,图谱没有磷酸铁锂的特征衍射峰,表明滤渣碳中不存在显著含量的磷酸铁锂;此外,采用滴定法测定的LiFePO₄/C中铁含量扣除红外碳硫仪测定的碳含量后,得到的LiFePO₄中铁含量与其理论含量相近;而且对碳渣洗涤液中的铁含量采用ICP-AES法分析,均显示未检出,进一步证明减压过滤除碳操作没有造成磷酸铁锂损失。对3个LiFePO₄/C实际样品中铁含量进行分析,结果的相对标准偏差均不大于0.06%;对减压过滤除碳后的溶液采用滴定法与ICP-AES法进行分析,测定结果的相对误差小于0.50%。由于ICP-AES法对高含量组分测试结果的稳定性相对较差,因此实验方法更适合规模化生产LiFePO₄/C中铁含量的测定。

Influence of vacuum filtration decarbonization on the determination of iron in carbon-coated lithium iron phosphate

The presence of carbon might affect the dissolution of carbon-coated lithium iron phosphate . Vacuum filtration decarbonization could benefit the determination of iron in carbon-coated lithium iron phosphate (LiFePO₄/C). In order to check out whether the decarbonization affect the determination results, the sample was dissolved in hydrochloric acid under 160 ℃ for 10 min, before vacumm decarbonization, potassium dichromate oxidation and titanium trichloride reduction titration determination of Fe in the material. X-ray diffraction(XRD) characterization showed the XRD spectrum of carbon residue and amorphous carbon were quite similar and characteristic peak was not observed, indicating the abscence of lithium iron phosphate. In addition, deducting the carbon content, iron content by titration is similar to theoretical content. Iron content in carbon slag solution was determined with ICP-AES, indicating non-detected, which further denied the loss of lithium iron phosphate during decarbonization. Analysis was conducted on Fe of three LiFePO₄/C practical samples. The relative standard deviation(RSD) was not more than 0.06%. When the solution was analyzed by titration and ICP-AES after vacuum filtration,the relative error was lower than 0.50%. Since the testing result of high-content component by ICP-AES was not quite stable, this method is more suitable to the determination of iron in carbon-coated lithium iron phosphate with mass production.