Tough and self-healable double-network hydrogel for environmentally resistant all-in-one supercapacitors and strain sensors

Flexible supercapacitors based on hydrogel electrolytes are promising power sources for wearable devices but suffer from high interfacial resistance and other drawbacks. To address this problem, we herein prepared a tough poly(vinyl alcohol)-gelatine double-network hydrogel electrolyte and endowed it with self-healability and low interfacial resistance through the introduction of reversible boronic ester bonds, glycerol, and ammonium sulphate. The in situ deposition of a conductive polypyrrole layer on the hydrogel surface afforded an all-in-one supercapacitor with decreased electrode–electrolyte interfacial resistance. The performance of this supercapacitor (areal capacitance = 1325.5 mF cm−2 at a current density of 1 mA cm−2, maximum energy density = 168.5 μW h cm−2, maximum power density = 670 μW cm−2) was superior to that of most of integrated supercapacitors reported to date and was hardly affected by low temperatures, long-term storage, bending, or self-healing after damage. Moreover, a biocompatible strain sensor based on the above hydrogel was used to detect the motion of human (face, elbow, knee) and mouse (thigh) models and thus monitor their behaviour and activity levels. Thus, the multifunctional integration of our dual-network hydrogel was concluded to hold considerable promise for the fabrication of wearable devices.