Mechanically Robust, Thermally Stable, and Fully Bio-Sourced Eutectogel Electrolytes for MXene-based Flexible Supercapacitor

Environmentally benign novel quasi-solid-state gel electrolytes comprising gelatin and an eco-friendly deep eutectic solvent (DES) or DES-water mixtures (water content ~20 wt% and 50 wt%) have been prepared and characterized. Depending on the content of gelatin and water in DES, the prepared eutectogels demonstrated significant ionic conductance, great stretch-ability (up to ~200%), mechanical robustness, shape-memory effect, thixotropy, multi-adhesiveness, non-flammability, optical transparency, and thermal stability in a wide-temperature range of (-20 to 150 ℃). Eutectogels further exhibit excellent electrochemical properties, which prompted their utilization as quasi solid-state gel electrolytes in symmetric supercapacitor having MXene based electrodes. This along with the improved interfacial contact between the electrodes and gel electrolyte resulted in a supercapacitor with energy density of 34 Wh Kg-1 even at a very high-power density of 14.4 kW Kg-1. The optimized eutectogel electrolyte-based supercapacitor has a capacitance of 113.13 F g-1 at the slowest scan rate of 10 mV s-1 and 17.01 F g-1 at a fast scan rate of 180 mV s-1, underscoring its suitability for applications demanding quick charge and discharge cycles, which remains stable at least up to 2000 charge-discharge cycles with 95% of the capacitance retention. Therefore, due to their multifunctional features, these bio-sourced gel electrolytes have the potential to be promising electrolytes for a range of next-generation stretchable electronics and energy storage devices.