Development of a Lithium Ion Cell Enabling In Situ Analyses of the Electrolyte by Gas Chromatography-Mass Spectrometry

摘要

Within the context of lithium ion batteries (LIB) the elucidation of occurring aging phenomena is of special interest. Therein the aging of the electrolyte, which is in contact with all parts of the LIB, typically represents a good indication of the overall cell status. Nevertheless, state of the art sample preparation for electrolyte analysis requires the mechanical opening of the cell and subsequent electrolyte extraction. Thus, the cells are destroyed during sample preparation and it is not possible to achieve data for multiple different states of health (SOHs) of one specific cell. In case of large cell formats the LIB has to be discharged prior to cell opening and electrolyte extraction further limiting the information to 0% state of charge (SOC). However, several analytical techniques are known, which do not rely on liquid samples, but may provide information about the electrolyte. In this case study an automated sample pretreatment was investigated, which was developed in the work group of Prof. Pawliszyn. The solid phase microextraction (SPME) in combination with gas chromatography mass spectrometry (GC-MS) provides several benefits with regard to the LIB environment - namely the headspace sampling option, the preconcentration of volatile organic compounds (VOCs) at room temperature and the small amount of removed sample.[3] This work reports on the development of a prototype round cell (18650 format) for in situ investigations of the electrolyte. The consumption of vinylene carbonate (VC) and emerging decomposition products have been analyzed at different SOHs. Furthermore, the cell setup provides the possibility to investigate the electrolyte during the formation. In this context sampling was performed at different voltage steps throughout the formation protocol or online while the cell was formatted.