线性滴定法测定六氟磷酸锂电解液中游离酸

六氟磷酸锂(LiPF₆)电解液中的游离酸含量是影响锂离子电池性能的一项重要指标,需要及时对其含量进行测定。因LiPF₆电解液热稳定性差,在常温下水解,实验提出了在低温条件下,采用等量加入的线性滴定法测定LiPF₆电解液中游离酸含量的方法。以氢氟酸-碳酸酯溶液为试验对象,测定出氢氟酸在0 ℃时的形成常数,作为后续计算的依据;控制测定温度在0 ℃左右,将0.50 mol/L KCl水溶液与LiPF₆电解液样品按体积比1∶1混合得到测试液,以0.010 mol/L NaOH标准滴定溶液进行滴定,至pH 7.0为终点;通过Johansson函数式计算并做图,进而得到滴定终点,再求得电解液中游离酸含量。探讨了常用添加剂和LiPF₆电解液中的碳酸酯有机溶剂对测定的影响,结果表明,这两者对测定结果的影响可忽略。将实验方法用于实际样品分析,测定结果与电位滴定法基本一致,相对标准偏差(RSD,n=5)在0.35%~1.1%之间,加标回收率在99.6%~101%之间。

Determination of free acid in lithium hexafluorophosphate electrolyte by linear titration

The content of free acid in the electrolyte of lithium hexafluorophosphate (LiPF₆) is an important index influencing the performance of lithium-ion battery, so it should be timely determined. Since the thermal stability of LiPF₆ electrolyte is poor and easily hydrolyzed at room temperature, a method for the determination of free acid content in LiPF₆ electrolyte by linear titration with equal addition amount was proposed at low temperature. Hydrofluoric acid-carbonate ester solution was used as testing objective in experiments. The formation constant of hydrofluoric acid at 0 ℃ was determined and used as the basis for the subsequent calculations. The measurement temperature was controlled to be about 0 ℃. Then 0.50 mol/L KCl solution was mixed with LiPF₆ electrolyte sample at the volume ratio of 1∶1 to prepare the testing solution. 0.010 mol/L NaOH standard solution was used as the titrant, and pH 7.0 was the endpoint. Johansson function was used for calculation and plotting to obtain the endpoint of titration. Finally, the content of free acid in electrolyte was obtained. The effect of common additives and carbonate solvents in LiPF₆ electrolyte on the determination was discussed. The results showed that their influences could be ignored. The proposed method was applied for the analysis of actual samples, and the found results were basically consistent with those obtained by the potentiometric titration. The relative standard deviations (RSD, n = 5) of determination results were between 0.35% and 1.1%, and the spiked recoveries were between 99.6% and 101%.