Moisture‐Assisted Silylation Triggered by Silicone Adhesives: A Hidden Electrolyte Decomposition Mechanism in Supercapacitors

Silicone adhesives in polyimide (Kapton) tape are revealed as hidden initiators of electrolyte decomposition in commercial-scale supercapacitors employing acetonitrile-based electrolytes. This study uncovers a previously unrecognized, moisture-assisted silylation mechanism in which silicone-derived trimethylsilyl species react with acetamide, a hydrolysis product of acetonitrile, in the presence of triethylamine (TETA), forming trimethylsilyl acetamide (TMSA) via nucleophilic substitution. This degradation pathway, activated under elevated voltage (≥4.1 V) and trace moisture, is distinct from known electrode-induced processes and accelerates electrolyte breakdown. A suite of analytical techniques, including gas chromatography-mass spectrometry (GC-MS), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), and electrochemical testing, unambiguously identifies the silicone adhesive as the primary source of reactive silicon. Control experiments confirm that TMSA formation requires both silicone adhesives and water, validating the proposed mechanism. These findings challenge the conventional assumption that non-electroactive components are chemically inert and demonstrate that auxiliary materials can drive parasitic side reactions under realistic abuse conditions. This work highlights the critical importance of full-system material compatibility screening in supercapacitor design and provides mechanistic insight for enhancing device longevity and safety.