A double cross-linked hydrogel electrolyte with high mechanical strength and excellent electrochemical performance for flexible supercapacitor and zinc ion capacitor

A biomass hydrogel electrolyte with double cross-linked structure was successfully fabricated by in situ polymerization and cross-linking reaction using polyacrylamide (PAAm) as the main network and gelatin as the reinforced network. This as-prepared gelatin/PAAm hydrogel electrolyte exhibits excellent mechanical strength (compressive, tensile strain and stress of GP-10 can reach 80 %, 1700 % and 10.4 MPa respectively) and high ionic conductivity. Flexible supercapacitors (FSCs) based on the gelatin/PAAm hydrogel electrolytes deliver a high specific capacitance of 140 F g−1 and excellent energy density of 49.8 Wh kg−1. More importantly, the FSCs not only achieve a long life of 50,000 cycles in a stable environment but also deliver high specific capacitance and good cycle performance when cycled at different folded angles. The constructed zinc ion capacitors (ZICs) applied with the gelatin/PAAm hydrogel electrolytes can achieve capacity retention of 98.0 % after 10,000 cycles at a high current density of 1 A g−1. These results demonstrate that the biomass hydrogel electrolytes exhibit excellent electrochemical performance and durability in flexible energy storage devices.