尖晶石钛酸锂(Li₄Ti₅O₁₂)作为锂离子电池负极材料在充放电过程中电压高, 体积变化可以忽略,具有极好的循环寿命、 热稳定性和安全性, Li₄Ti₅O₁₂中金属杂质元素的迁移以及沉积都是已知的有害降解效应,尤其是磁性金属杂质元素的存在会导致材料的自放电, 同时可能造成电池内部的微短路, 进而影响电池的安全性能和循环寿命。该研究提出了采用微波等离子体原子发射光谱(MP-AES)测定Li₄Ti₅O₁₂中金属杂质元素的新方法。采用王水溶液为消解试剂对Li₄Ti₅O₁₂样品进行微波消解, 样品溶液无需过滤, 直接采用MP-AES测定其中的金属杂质元素Mn, Na, Pb, Ni, Cr, Zn, K, Fe, Al, Mg, Cu, Ca, Co和Cd。选择波长Mn 403.076 nm, Na 589.592 nm, Pb 405.781 nm, Ni 352.454 nm, Cr 425.433 nm, Zn 213.857 nm, K 766.491 nm, Fe 371.993 nm, Al 396.152 nm, Mg 285.213 nm, Cu 324.754 nm, Ca 393.366 nm, Co 340.512 nm和Cd 228.802 nm为分析谱线, 结合快速线性干扰校正(FLIC)技术, 不仅校正了谱线重叠干扰, 而且还校正了所有分析元素的背景干扰。加入CsNO₃为电离抑制剂, 校正了易电离Li基质产生的电离干扰。 选择 Y为内标元素, 校正了分析信号强度的不稳定和基体效应。方法的检出限(MDL)为0.03~0.77 μg·g^-1, 线性相关系数≥0.999 3, 加标回收率为96.4%~103%, 相对标准偏差(RSD)≤3.89%, 采用所建立的分析方法对实际样品进行分析, 并与国标法(GB/T 30836—2014)进行对比分析, 经 t检验法统计分析表明, 在95%的置信度水平, 除元素Zn以外, 其余元素的测定结果与国标法无显著性差异, 进一步验证了方法的准确性好。 使用氮气为等离子体气体的MP-AES与使用氩气为等离子体气体的电感耦合等离子体发射光谱(ICP-OES)相比较, 可以显著降低运行成本,与使用可燃气体和氧化性气体的原子吸收光谱(AAS)相比较, 安全性更高,稳定性更好。该方法操作简单、分析成本低、准确性高、精密度好, 为Li₄Ti₅O₁₂中多种金属杂质元素的高通量测定提供了新方法。

The spinel Li₄Ti₅O₁₂ demonstrates high operating potential, excellent cycle life, and high safety as anode material of lithium-ion battery due to its negligible volume change, high thermal stability. The migration and deposition of metal impurities in Li₄Ti₅O₁₂ are harmful degradation effects. In particular, magnetic metal impurities will cause the self-discharge and micro short circuit inside the battery, thereby affecting the safety performance and cycling life of the battery. A new method was proposed to determining the metal impurities in Li₄Ti₅O₁₂ by microwave plasma atomic emission spectroscopy (MP-AES). The metal impurities of Mn, Na, Pb, Ni, Cr, Zn, K, Fe, Al, Mg, Cu, Ca, Co, and Cd was determined by MP-AES via dissolving the Li₄Ti₅O₁₂ sample in aqua regia solution by microwave digestion without further filtration. The wavelengths of Mn 403.076 nm, Na 589.592 nm, Pb 405.781 nm, Ni 352.454 nm, Cr 425.433 nm, Zn 213.857 nm, K 766.491 nm, Fe 371.993 nm, Al 396.152 nm, Mg 285.213 nm, Cu 324.754 nm, Ca 393.366 nm, Co 340.512 nm, and Cd 228.802 nm was selected as the analytical line. Combined with the fast linear interference correction (FLIC) technology, the spectral interference and the background interference of all analytes was corrected. CsNO₃ was added as an ionization suppression solution to correct the ionization interference caused by the easily ionized Li matrix. Y was used as the standard internal element to correct for signal intensity instability and matrix effects. The method detection limit (MDL) was 0.03~0.77 μg·g^-1, the linear correlation coefficient was all greater than 0.999 3, the spiked recoveries were 96.4%~103%, and the relative standard deviations (RSDs) were less than 3.89%. The developed method was used to analyze the real sample and compared it with the national standard method (GB/T 30836—2014). Statistical analysis by the t-test method showed that at the 95% confidence level, there were no significant differences in most of the elements between the MP-AES and GB/T 30836—2014 methods, except for Zn, which further verifies the high accuracy of the method. Compared with inductively coupled plasma optical emission spectroscopy using argon as plasma gas, employing nitrogen as plasma gas can significantly reduce the operation cost. MP-AES has higher safety and better stability than atomic absorption spectroscopy using combustible gas. This method is simple to operate, low cost of analysis, high accuracy, and good precision. It provides a new method for the high-through put determination of multiple metal impurity elements in Li₄Ti₅O₁₂.