Mechanically robust, thermally stable, bio-sourced and flexible eutectogel electrolytes for MXene-based symmetric supercapacitors

Abstract

Environmentally benign and 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. The prepared eutectogels demonstrated significant ionic conductance, great stretchability (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 °C. Eutectogels further exhibit excellent electrochemical properties, which prompted their utilization as quasi-solid-state gel electrolytes in symmetric supercapacitors having MXene-based electrodes. An improved interfacial contact between the electrodes and the gel electrolyte resulted in a supercapacitor with an energy density of 34 Wh kg⁻¹ even at a very high power-density of 14.4 kW kg⁻¹. The optimized supercapacitor exhibits a capacitance of 113.13 F g⁻¹ at a slow scan rate of 10 mV s⁻¹ and 17.01 F g⁻¹ at a fast scan rate of 180 mV s⁻¹, highlighting its potential for rapid charge–discharge applications. It maintains stability for at least 8000 charge–discharge cycles with 92.10% capacitance retention. Therefore, due to their multifunctional features, these bio-sourced gel electrolytes have the potential to be promising electrolytes for a variety of stretchable electronics and energy storage devices.