Monitoring gas evolution during ageing of industrial supercapacitors studied by in situ GC-MS

Understanding gas evolution during the ageing of electrical double layer capacitors (EDLCs) is critical for improving long-term performance and safety. However, direct gas analysis in industrial-scale cells has been hindered by their sealed design, complex internal structure, and small gas volumes. This study aimed to develop and validate a novel in situ gas chromatography–mass spectrometry (GC–MS) method capable of analysing gas evolution in intact, industrial-format supercapacitor cells under realistic ageing conditions. A custom stainless-steel jig with a detachable gas extraction piece was designed to enable controlled, on-demand sampling from cylindrical EDLCs undergoing an accelerated floating ageing protocol at 3.0 V and 65°C. The system was evaluated for mechanical stability and non-intrusiveness through electrochemical performance metrics and internal pressure monitoring, while extracted gases were analysed qualitatively by GC–MS. The integrated sampling hardware maintained normal ageing behaviour, with capacitance fading, coulombic efficiency, and logarithmic pressure growth comparable to unmodified cells. The developed in situ GC–MS technique bridges the gap between model-cell studies and real supercapacitor devices, enabling direct correlation of molecular-level gas formation with macroscopic ageing behaviour. This reliable approach provides a versatile platform for investigating alternative electrolytes, electrode materials, and ageing conditions, paving the way for deeper mechanistic understanding of supercapacitor degradation.