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 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 TEABF 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 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.