Preparation of dual cross-linked hydrogel electrolytes containing modified lignin for supercapacitors and sensors

Hydrogel electrolytes have the dual functions of electrolyte and separator and combine the advantages of liquid and solid electrolytes, making them one of the most ideal candidates for supercapacitors and sensors. However, hydrogel electrolytes are prone to deactivate when the operating temperature is too low. Therefore, dual cross-linked hydrogels with chemical bonds and multiple noncovalent interactions were prepared at room temperature using activated modified lignin. Dual cross-linked hydrogel had excellent mechanical performance and fatigue resistance, whose tensile elongation could reach 700 %. Because the hydrogel contained a concentrated alkaline solution, the electrolyte achieved excellent freezing resistance and a high ionic conductivity of 0.345 S cm-1 (-40 degrees C, 0.044 S cm-1). Supercapacitors assembled with the hydrogel electrolyte demonstrated a high specific capacitance of 210 F g-1 (-40 degrees C, 176 F g-1) at 1.0 A g-1. Furthermore, the hydrogel electrolyte exhibited good electrochemical properties not only in alkaline environments but also in neutral and acidic conditions. The hydrogel could also act as a flexible sensor with a sensitivity of 1.34 within a 100 % strain, making it a promising material for wearable sensors to monitor joint activities in the human body.