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-1, which was greatly higher than gel polymer electrolyte based on original pure SPI (1.84 mS cm-1). More significantly, supercapacitors constructed by grafting-modified SPI delivered a specific capacitance of 141.74 F g-1 at 1.0 A g-1 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-1 at a current density of 0.5 A g-1. 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.