Converting soy protein isolate into biomass-based polymer electrolyte by grafting modification for high-performance supercapacitors.

Soy protein isolate (SPI) is one of the most abundant plant proteins in nature. Enormous studies have been carried out on SPI-based materials, however, the application for energy storage devices is still limited due to its fiddly film forming process and lack of electrochemical performance. Herein, we presented a SPI-based polymer electrolyte by grafting modification with the hydrophilic functional monomer acrylamide (AM). The optimized gel polymer electrolyte (GPE) exhibited an excellent ionic conductivity up to 5.10 mS cm, which was greatly higher than gel polymer electrolyte based on original pure SPI (1.84 mS cm). More significantly, supercapacitors constructed by grafting-modified SPI delivered a specific capacitance of 141.74 F g at 1.0 A g and exhibited high capacitance retention of 95% after 8000 charge-discharge cycles. Beyond that, redox-active polymer electrolyte based on grafting-modified SPI combining with KI enormously improved the energy density of supercapacitor up to 27.52 Wh kg at a current density of 0.5 A g. This work provided a novel and facile strategy to obtain a high-performance SPI-based polymer electrolyte and laid an experimental foundation for the high-value application of SPI in the field of energy storage devices.