Studying Aging of Lithium Ion Batteries – Observing Gas Evolution with in-Operando Mass Spectrometry

Abstract

Increasing our understanding on different aging processes and mechanisms linked to the lifetime and safety of lithium ion batteries is crucial for extending their usability in e.g. hybrid and electric vehicles followed by potential 2nd life applications. Coupling a mass spectrometer (MS) to a special on-line electrochemical cell hosting battery components enables time resolved detection of gases that are evolving during cycling and other aging. Gas evolving processes are for example decomposition of the electrolyte, formation of the SEI (solid electrolyte interphase) and other side reactions [1-3]. In this work, an in-house made adjustable electrochemical in-operando cell with a connection to the MS is used to study aging-related gas evolution at two types of cells: laboratory-scale lithium ion batteries and larger commercial cylindrical batteries. The design of the in-operando cell is flexible for different battery chemistries and to some extent different sizes. The commercial cylindrical cells used in this study are NMC-based Li-ion batteries. The battery can is pierced to allow gas diffusion inside the leak-tight housing connected to the MS. Aging of the large batteries can be inhomogeneous [4] and therefore it is highly interesting to measure the gas evaluation also from large cells and compare these to small laboratory-scale cells aged at more defined conditions. For the commercial batteries, the possibility to perform long term aging experiments is desirable. The cell construction used in this work allows replacing the gas sampled from the cell head-space, ensuring constant pressure in the measurement chamber and enabling prolonged measurements. A safety valve is installed to release overpressure in case of an extensive gas evolution. The goal of the presented work is to quantify gaseous products evolving upon battery aging with different operating parameters such as rate of charging [5], temperature, state of charge and voltage window to gain more insight to the aging phenomena. [1] S. Meini, M. Piana, N. Tsiouvaras, A. Garsuch, H.A. Gasteiger, Electrochemical and Solid-State Letters 15(4) (2012) A45-A48. [2] B.B. Berkes, A. Jozwiuk, M. Vracar, H. Sommer, T. Brezesinski, J. Janek, Analytical Chemistry 87(12) (2015) 5878-5883. [3] D. Streich, A. Gueguen, M. Mendez, F. Chesneau, P. Novak, E.J. Berg, Journal of the Electrochemical Society 163(6) (2016) A964-A970. [4] M. Klett, P. Svens, C. Tengstedt, A. Seyeux, J. Swiatowska, G. Lindbergh, R. Wreland Lindstroem, J. Phys. Chem. C 119(1) (2015) 90-100. [5] A.S. Mussa, M. Klett, M. Behm, G. Lindbergh, R.W. Lindström, Journal of Energy Storage 13 (2017) 325-333.