For decades great efforts have been devoted to Lithium-Ion Batteries (LIB) with the goal to improve performance and further strengthen their market position in mobile and grid energy storage applications. Due to high volumetric and gravimetric energy, high power density, and long cycle life, an increasing number of large battery packs was demanded by the automotive sector to fulfil new carbon emission standards around the globe.

To achieve the required energy density and longevity, the study of interaction between novel anode and high voltage cathode materials with the electrolyte raised interest throughout the research community. The combination of organic electrolytes with increased cell dimensions for consumer products also sparked attention regarding safety and cell stability, due to the formation of flammable, corrosive, and toxic gases. Potential risk must be assessed with respect to the formation of volatile and reactive gas species during cell operation which originate from the decomposition of electrolyte and passivation layers that can negatively impact the cell performance. The analysis of gases deriving from decomposition reactions in batteries and in particular the employment of gas chromatography / mass spectrometry (GC / MS) has been proven to be reliable for the investigation of degradation phenomena. Unfortunately, conventional gas chromatographs lack in separation speed for operando testing of fast processes, for example battery failure. Therefore, we developed an operando gas analysis method which allows an increased sampling number leading to improved time resolution and therefore permitting insight into fast cell degradation processes.

Here, we present operando GC / MS as a technique for monitoring the evolution of volatile organic compounds arising from the degradation of conventional LIB cells. The operando analysis of complex gas mixtures was achieved by the combination of a continuous sampling technique and GC / MS. Commercially produced pouch-cells and coin cell- sized batteries were subjected to operando measurements that enabled the investigation of evolved gas species with respect to the battery potential. Particular attention was paid to decomposition products derived from carbonate- based electrolytes and processes related to the degradation of LiPF₆ during battery operation.

The author gratefully acknowledges the FFG (Austrian Research Promotion Agency) for funding this research within project No. 879613.