Ionogel-Based Electrodes for Non-Flammable High-Temperature Operating Electrochemical Double-Layer Capacitors

The design of interfaces between nanostructured electrodes and advanced electrolytes is critical for realizing advanced electrochemical double-layer capacitors (EDLCs) that combine high charge-storage capacity, high-rate capability, and enhanced safety. Toward this goal, this work presents a novel and sustainable approach for fabricating ionogel-based electrodes using a renewed slurry casting method, in which the solvent is replaced by the ionic liquid (IL), namely 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI). This method avoids time-consuming and costly electrolyte-filling steps by integrating the IL directly into the electrode during slurry preparation, while improving the rate capability of EDLCs based on pure non-flammable ILs. The resulting ionogel electrodes demonstrate exceptional electrolyte accessibility and enable the production of symmetric EDLCs with high energy density (over 30 Wh kg^-1 based on electrode material weight) and high-rate performance. These EDLCs could operate at temperatures up to 180 °C, far exceeding the limitations of traditional EDLCs based on organic electrolytes (e. g., 1 M TEABF₄ in acetonitrile, up to 65 °C). Ionogel-type EDLCs exhibit remarkable long-term stability, retaining 88 % specific capacity after 10000 galvanostatic charge/discharge cycles at 10 A g^-1 and demonstrating superior retention compared to conventional EDLCs (50 %), while also maintaining 92.4 % energy density during 100 h floating tests at 2.7 V. These electrochemical properties highlight their potential for robust performance under demanding conditions. This study highpoints the practical potential of ionogel-based electrodes to advance IL-based EDLC technology, paving the way for next-generation energy storage devices with high-temperature and high-voltage operational capabilities.