Determination and quantification of cations in ionic liquids by capillary electrophoresis-mass spectrometry.

In this study, a capillary electrophoresis (CE) method hyphenated to a high-resolution mass spectrometer is presented to detect the cations in ionic liquids (ILs) and their decomposition products. The investigated ILs were 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR13TFSI), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM TFSI). With this method, it was possible to achieve baseline separation of the decomposition products from the main cations in short migration times. Because of the successful baseline separation, it was also possible to quantify the main cations in ILs, which were aged at room temperature and at 60°C. Additionally, the relative standard deviations (RSDs) for the concentrations of the main cations investigated by CE and ion chromatography (IC) were given to compare the both methods with each other. The concentrations were determined for the main cations aged at different temperatures. Finally, the limits of detection (LOD) and quantification (LOQ) were calculated for this method and compared to the IC results. The LODs and LOQs for CE method was in the range of 0.3-2.1mg/kg and for the IC method 34.9-455.2mg/kg. Therefore, more decomposition products of EMIM+ were determined by the CE method than by the IC method. In each investigated IL, more decomposition products of the cations were detected at 60°C compared to room temperature. The PYR14+ concentration decreased by 4 % at 60°C, while PYR13+ and EMIM+ decreased more than 10 % aged at 60°C in contrast to the sample which was aged at room temperature.

Decomposition of Imidazolium-Based Ionic Liquids in Contact with Lithium Metal.

Ionic liquids (ILs) are considered to be suitable electrolyte components for lithium-metal batteries. Imidazolium cation based ILs were previously found to be applicable for battery systems with a lithium-metal negative electrode. However, herein it is shown that, in contrast to the well-known IL N-butyl-N-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide ([Pyr14 ][TFSI]), 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C2MIm][TFSI]) and 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C4MIm][TFSI]) are chemically unstable versus metallic lithium. A lithium-metal sheet was immersed in pure imidazolium-based IL samples and aged at 60 °C for 28 days. Afterwards, the aged IL samples were investigated to deduce possible decomposition products of the imidazolium cation. The chemical instability of the ILs in contact with lithium metal and a possible decomposition starting point are shown for the first time. Furthermore, the investigated imidazolium-based ILs can be utilized for lithium-metal batteries through the addition of the solid-electrolyte interphase (SEI) film-forming additive fluoroethylene carbonate.

Capillary electrophoresis with contactless conductivity detection for the quantification of fluoride in lithium ion battery electrolytes and in ionic liquids-A comparison to the results gained with a fluoride ion-selective electrode.

In this study, an optimized method using capillary electrophoresis (CE) with a direct contactless conductivity detector (C4 D) for a new application field is presented for the quantification of fluoride in common used lithium ion battery (LIB) electrolyte using LiPF6 in organic carbonate solvents and in ionic liquids (ILs) after contacted to Li metal. The method development for finding the right buffer and the suitable CE conditions for the quantification of fluoride was investigated. The results of the concentration of fluoride in different LIB electrolyte samples were compared to the results from the ion-selective electrode (ISE). The relative standard deviations (RSDs) and recovery rates for fluoride were obtained with a very high accuracy in both methods. The results of the fluoride concentration in the LIB electrolytes were in very good agreement for both methods. In addition, the limit of detection (LOD) and limit of quantification (LOQ) values were determined for the CE method. The CE method has been applied also for the quantification of fluoride in ILs. In the fresh IL sample, the concentration of fluoride was under the LOD. Another sample of the IL mixed with Li metal has been investigated as well. It was possible to quantify the fluoride concentration in this sample.