Stretchable, self-healable and highly conductive natural-rubber hydrogel electrolytes for supercapacitors: Advanced wearable technology

Promising advancements in energy technologies lie in the development of highly flexible hydrogel electrolytes, which offer biodegradability, cost-effectiveness, and safety. However, striking a balance between stretchability, remarkable ionic conductivity, and self-healing ability remains challenging. In this research, we present a novel approach involving the utilization of epoxidized natural rubber (ENR)/acrylamide (AAm)/acrylic acid (AA) copolymer hydrogel electrolytes formed through a free radical mechanism. To further enhance the conductivity, hydrogel electrolytes were immersed in 1 M sodium sulfate (Na2SO4) salt solutions for varying periods. By capitalizing on the hydrogen bonding and electrostatic interactions within the hydrogels and the hydrogel-salt interaction, the resulting hydrogel exhibited an impressive ionic conductivity of 19.4 x 10-2 S/cm, a stretchability of 550 % from its initial length, and demonstrated self-healing capabilities. Additionally, employing symmetrical porous carbon electrodes, the hydrogel-based electric double layer capacitor (EDLC) achieved an outstanding specific capacitance of 55.65 F/g, enduring stable cycling over 3500 cycles without significant discharge. Notably, the mechanical strength of the hydrogel is significantly improved after the self-healing process. Importantly, this study highlights the significant role of immersion time in improving the ionic conductivity and functionality of hydrogel electrolytes.