Mechanically Robust, Thermally Stable, Bio-Sourced and Flexible Eutectogel Electrolytes for MXene-Based Symmetric Supercapacitor

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 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. An improved interfacial contact between the electrodes and 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 8,000 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.