Abstract:

An anti-freezing hydrogel electrolyte(SPI-PVA-PAAm/LiCl) was synthesized, in which soybean protein isolates (SPI), ployvinyl alcohol(PVA) and acrylamide(AAm) were used as raw materials, ammonium persulfate(APS) was used as the initiator, N, N'-methylenebisacrylamide(MBAA) was used as the covalent crosslinker, LiCl was used as the electrolyte salt, and N, N, N', N'-tetramethylethylenediamine(TEMED) was used as the accelerator. Under low temperature conditions, the mechanical properties of the hydrogel electrolyte were analyzed, and the electrochemical properties of the solid-state supercapacitor based on this hydrogel electrolyte were investigated. The results showed that the hydrogel electrolyte had excellent anti-freezing propertity, because a certain molar concentration of LiCl reduced the freezing point of pure water in the hydrogel electrolyte and inhibited the crystallization behavior of water molecules. When the environmental temperature was reduced from 25℃ to -20℃, the hydrogel electrolyte still showed good mechanical properties and ionic conductivity. With the increase of the amount of LiCl, the compression performance of the hydrogel electrolyte firstly increased and then decreased, and the ionic conductivity increased. After 10 cycles of 80% compression strain, the stress retention rate, plastic deformation rate and energy loss coefficient of the hydrogel electrolyte with LiCl concentration of 5 mol/L(S-Li-5) were more than 100%, less than 25% and 0.33, respectively. The hydrogel electrolyte with LiCl concentration of 15 mol/L(S-Li-15) and CNTs were used to assemble the solid supercapacitor whose electrochemical performance was evaluated. When the ambient temperature was reduced from 25℃ to -20℃, the specific capacitance of assembled supercapacitor calculated by GCD curve could be maintained above 80%, and 0-70% compression strain could be withstood without damage, and the supercapacitor could still work normally; In addition, when the current density was 8.12 A/g, the capacitance retention rate of the device was higher than 91% after 1 000 cycles at -20℃.

Key words: soybean protein, polyvinyl alcohol, hydrogel electrolyte, supercapacitor, anti-freezing