Analysis of the Failure Modes, Mechanisms, and Effects of Potassium Acetate Water-in-Salt Electrolyte-Based Supercapacitor

Water-In-Salt (WIS) electrolytes are expected to replace expensive, environmentally harmful organic electrolytes while delivering high voltages and improving system safety. In this study, analysis of the failure modes, mechanisms, and effects of a highly concentrated potassium acetate (KAc) electrolyte was conducted through electrolyte degradation at 2 V in a conventional EDLC carbon-based symmetric configuration. The adopted method provides a simplified yet effective approach for assessing the complexity and interconnectivity of degradation mechanisms in a WIS supercapacitor. The effects analysis included electrochemical stability studies, post-mortem characterizations (SEM-EDS and XPS), low-frequency impedance fitting, and cell reassembly using end-of-life electrodes. Among the failure modes analyzed, electrolyte decomposition and pore blocking exhibit strong physicochemical correlations and high failure rates. Therefore, they should be prioritized in the design of new WIS electrolyte compositions for next-generation energy storage systems.