Investigation of Electrolyte Decomposition Byproducts in Gas and Liquid Phases Due to Water Impurities in Large‐Scale Acetonitrile‐Based Supercapacitors

Abstract This study investigates the impact of water impurities on electrolyte decomposition in large‐scale cylindrical supercapacitors, with a focus on acetonitrile‐based electrolytes. The research identified ethylene, ethane, and nitrogen as primary gaseous byproducts and acetamide, N‐ethyl acetamide, and trimethylsilyl acetamide as major liquid‐phase decomposition products. Advanced analytical techniques, including in‐situ gas chromatography and nuclear magnetic resonance, revealed that water impurities significantly accelerate electrolyte degradation. The findings demonstrate that water‐induced decomposition mechanisms involve intricate pathways, including Hofmann elimination and hydrolysis reactions. Additionally, the presence of water catalyzes the formation of new byproducts, impacting both the electrolyte and electrode stability. This comprehensive analysis provides critical insights into the degradation processes of supercapacitors, emphasizing the need for stringent control of water content to enhance device longevity and performance. The study's outcomes suggest potential strategies for optimizing electrolyte compositions and electrode materials to mitigate degradation and improve supercapacitor efficiency.