Aging Investigations of Various Electrolytes By Means of IC/ESI-MS and CE/ESI-MS
In this work, the thermal decomposition products of electrolytes containing the widely used lithium hexafluorophosphate (LiPF6) as a conducting salt are investigated by two different developed separation methods: Ion Chromatography (IC) (see Figure 1) and Capillary Electrophorese (CE). Both separation methods are coupled by Electrospray Ionization Mass Spectrometer (ESI-MS) identifying developed decomposition products. In Figure 1, some decomposition products of LiPF6 are presented: hydrofluoric acid (HF) and difluorophosphate (PO2F2-) . We introduced the measurement method CE/ESI-MS for electrolytes to confirm the decomposition products of the already developed IC/ESI-MS method. Beyond that, CE has the advantage that only small amounts (nL range) of electrolytes for injection are required and that it is possible to measure cations and anions in the same measurement.
Most commercial available electrolytes in LIBs are based on organic solvents, there they are easily flammable and a safety risk for people and the environment in case of accident. Ionic liquids (ILs) are discussed as future electrolytes in LIBs because of theirs advantageous physical properties like non-flammability and non-volatility.For the application in future LIBs, it is important to gain more information about their thermal stability and the influence of lithium salts to the aging process of ILs.
Therefore, the effect of electrolyte salts like LiPF6 on the thermal decomposition of ILs is measured as well by our developed CE/ESI-MS and the new IC/ESI-MS methods. In Figure 2, the decomposition products of the ILs PYR13FSI and PYR13TFSI mixed with LiPF6 are illustrated. It is obvious that PYR13TFSI did not show any degradation products mixed with LiPF6, while PYR13FSI showed the following decomposition products: SO3F- and H2NO3S-.
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