Molecularly engineered chitosan-derived poly(aprotic/protic ionic liquids) double-network hydrogel electrolytes for flexible supercapacitors and wearable strain sensors

Polymeric conductive hydrogels have been highlighted for use in flexible electronics, and there is still a challenge to design and fabricate a high-performance hydrogel electrolyte with integrated and multiple properties, such as sustainability, stretchability and compressibility, ionic conductivity, antibacterial property, strain sensitivity, and low-temperature tolerance. Herein, chitosan (CS) derived poly(aprotic/protic ionic liquids) (CS-PAPILs) are facilely prepared by taking the structural and sustainable features of chitosan and betaine hydrochloride, which are used as a functional component for the fabrication of CS-PAPILs/polyacrylamide (PAM)/LiCl (CS-PAPILs/PAM/LiCl) double-network (DN) hydrogel electrolyte via an in situ polymerization of AM and then a soaking strategy in LiCl aqueous solution. The achieved DN hydrogels exhibit tunable mechanical performance (tensile strength of 70–900 kPa, elastic modulus of 31.5–484 kPa, high compressibility (4450 kPa at 80 % strain), superior low-temperature tolerance (freezing point < -85 °C), anti-dehydration performance, high ionic conductivity at 25/-50 °C (94.8/4.6 mS cm −1 ), and excellent antibacterial activity. As a proof of concept, an assembled flexible and anti-freezing supercapacitor by the as-prepared DN hydrogel electrolyte demonstrated a high specific capacitance of 108.4F/g (at 2 A/g) and impressive cycling stability over 50,000 cycles at temperature as low as −50 °C. Furthermore, a wearable strain sensor based on the DN hydrogel was also demonstrated, and the sensor can be successfully attached to the human joints to monitor various human motions.