Lithium ion battery electrolyte degradation of NMC622||AG and NMC811||AG+SiOx cells using chromatographic analytical techniques

Kessen, Dennis; Fehlings, Nick; Lechtenfeld, Christian-Timo; van Wickeren, Stefan; Winter, Martin; Nowak, Sascha; Wiemers-Meyer, Simon

Zusammenfassung

Poster Abstract PhD Day 22.09.2023 Lithium ion battery electrolyte degradation of NMC622||AG and NMC811||AG+SiOx cells using chromatographic analytical techniques Dennis Kessena,*, Nick Fehlingsa, Christian Lechtenfelda, Stefan van Wickerena, Martin Wintera,b, Sascha Nowaka, Simon Wiemers-Meyera a University of Münster, MEET Battery Research Center, Corrensstraße 46, 48149 Münster, Germany b Helmholtz-Institute Münster, IEK-12, FZ Jülich, Corrensstraße 46, 48149 Münster, Germany One major challenge of lithium ion batteries (LIBs) is the degradation of the cell components during operation and storage which reduces both storage- and cycle lifetime. The so-called aging is significantly related to the decomposition of the liquid electrolyte, which is in contact to every constituent of the LIB.[1] It is manifested by electrolyte consumption, gas formation and ultimately drying out of the cell. Besides formation of the solid electrolyte interphase, ring-opening of the cyclic ethylene carbonate and subsequent reactions with linear carbonates lead to the formation of oligomeric decomposition species.[2] Thermal and electrochemical instability of the conducting salt LiPF6 further lead to hydrolysis, and hence the formation of potentially toxic organophosphates and organofluorophosphates.[3] Gas, liquid and ion chromatography (GC, LC, IC) with hyphenation to high resolution mass spectrometry (HRMS) are established methods for the structural analysis of electrolytes and their decomposition products.[4] In this study, 1 Ah pouch cells (Li-FUN Technology Ltd., China) with the cell chemistries NMC622||AG and NMC811||AG+SiOx (20 %) were analysed after formation and calendric aging at 60 °C with 100 % state of charge. Mixtures of vinylene carbonate, fluoroethylene carbonate and lithium bis(oxalato)borat were used in addition to the baseline electrolyte EC/EMC 3/7 (w/w) % + 1M LiPF6. By using GC, LC and IC, a comprehensive qualitative and quantitative analysis of permanent gases as well as ionic and non-ionic decomposition species was obtained. [1] J. Vetter, P. Novák, M. R. Wagner, C. Veit, K.-C. Möller, J. O. Besenhard, M. Winter, M. Wohlfahrt-Mehrens, C. Vogler, A. Hammouche, Journal of Power Sources 2005, 147, 269. [2] J. Henschel, C. Peschel, S. Klein, F. Horsthemke, M. Winter, S. Nowak, Angewandte Chemie International Edition 2020, 59, 6128. [3] S. Nowak, M. Winter, Journal of The Electrochemical Society 2015, 162, A2500-A2508. [4] Y. P. Stenzel, F. Horsthemke, M. Winter, S. Nowak, Separations 2019, 6, 26. ​​​​​​​