Protein-based hydrogel electrolytes for stretchable Zn-ion batteries

Abstract: Stretchable aqueous-based Zn-ion batteries have shown promise as a sustainable and safe energy storage system for wearable electronics used in healthcare, sports, soft robotics, and prosthetics. A battery consists of the active electrode, electrolyte, current collector, and encapsulation. In this work, we focus on the development of the electrolyte component, which is a hydrogel based on polymers. Natural polymers (e.g proteins, polysaccharides) are chosen over synthetic ones because they are biodegradable, abundant in nature, and environmentally sustainable. Here, a hydrogel based on gelatin (G) and kappa-carrageenan (kC) were prepared and evaluated. We observed that the addition of kC into the hydrogel composite improved its mechanical properties. Optimum conditions at weight ratios of G:kC -99:1 wt%, the hydrogel showed good mechanical strength with an elongation at break of 370 ± 28%, elastic modulus of 0.119 ± 0.0256 MPa, and reversibility during 100 cyclic stretching at 50% strain. The hydrogel had a reasonable ionic conductivity of 14.80 mS/cm and was successfully integrated into a battery with a capacity of 0.24 mA/cm2.