Preparation Of Polymer Electrolytes Based On Graft-Modified Soy Protein Isolate And Study On Performance Of Supercapacitors

With the advancement of science and technology,electronic devices are gradually miniaturized,and liquid electrolytes cannot fully meet the requirements of supercapacitors due to safety and volume problems.Polymer electrolytes that have the dual functions of transporting ions and blocking electrons have developed rapidly.Polymer matrix as its skeleton seriously affects the performance of the devices.At present,most of the polymer matrix materials are non-degradable synthetic polymer materials,which do not conform to the concept of green environmental protection.Therefore,biomass materials as matrix materials have attracted attention.Soy protein isolate(SPI)is a natural polymer material with a wide range of sources,which has the characteristics of film formation and hydrophilicity.SPI is rich in reactive functional groups such as amino and hydroxyl groups,which could be designed and modified to produce polymer matrix materials with excellent performance according to application requirements.The process of grafting modification is controllable and attracts much attention.Compared with the secondary battery,the energy density of supercapacitors is still low,and introducing redox active materials into polymer electrolyte is an effective method to increase the energy density of supercapacitor.In summary,this paper SPI was used as the polymer electrolyte matrix material,and improves the electrochemical performance of supercapacitor by adding redox active materials and grafting two different monomers.A series of redox polymer electrolytes with different contents of KI were prepared by combining SPI as the matrix material with lithium sulfate(Li2SO4),a neutral electrolyte with a wide potential window,and adding different masses of redox active material potassium iodide(KI).(1)When the mass of KI added accounts for 100%of the mass of Li2SO4,the ionic conductivity of GPE-100 wt%KI could reach 2.54 mS cm-1,which was 30.93%higher than that of the polymer electrolyte without KI.(2)A series of supercapacitors(SC-x wt%KI)were assembled by GPE-x wt%KI and commercial activated carbon electrodes.SC-100wt%KI had the most excellent electrochemical performance,the single electrode specific capacitance and energy density increased significantly.The single electrode specific capacitance and energy density increased by about 3 times at a current density of 0.8 A g-1,which were 224.20 F g-1 and 16.02 W h kg-1,respectively.(3)The electrochemical performance of SC-100 wt%KI had almost no change at different angles,indicating its excellent flexibility.Three SC-100 wt%KI in series provided energy for LED for several minutes,indicating that it has good application performance.After 1500 continuous charge and discharge cycles,the capacitance value was still greater than that of the supercapacitor without KI.In order to improve the affinity between the SPI and the electrolyte,and improve the electrochemical performance of supercapacitor.A series of modified SPI-based polymer electrolytes(GPE-SPI-g-PMAA-X)and supercapacitors(SC-SPI-g-PMAA-X)were prepared by grafting modified SPI with different contents of methacrylic acid(MAA)and introducing hydrophilic functional groups—carboxyl groups.(1)When the added amount of MAA was twice the quality of SPI,it has the best overall performance.The ion conductivity of GPE-SPI-g-PMAA-2 was 4.72 mS cm-1,which was 157.92%higher than that of GPE-SPI.(2)The electrochemical performance of SC-SPI-g-PMAA-2 had been improved,the single electrode specific capacitance and energy density of SC-SPI-g-PMAA-2 were 132.63 F g-1 and 9.83 W h kg-1 respectively at a current density of 0.5 A g-1.(3)SC-SPI-g-PMAA-2 had excellent flexibility,good applicability and cycle stability,and the electrochemical performance was better than that of a supercapacitor assembled from a commercially available hydrophilic PP/PE composite membrane.(4)After adding KI,the electrochemical performance of supercapacitor had been further improved,and the single electrode specific capacitance was enhanced by 162.02%and energy density by 168.43%at a current density of 1.0 A g-1.At present,polyacrylamide as the matrix material of polymer electrolyte has received extensive attention.Therefore,acrylamide(AM)was used as a functional monomer to graft modified SPI,different content of AM was grafted to SPI,and hydrophilic functional group amino was introduced to prepare modified SPI based polymer electrolytes.(1)When the mass of AM was twice that of SPI,it had the highest grafting rate,and GPE-SPI-g-PAM-2 had the largest ion conductivity of 5.10 mS cm-1.(2)The polymer electrolyte with the best performance and the activated carbon electrode were assembled into a supercapacitor SC-SPI-g-PAM-2,which had excellent electrochemical performance.The specific capacitance of a single electrode could reacd 145.88 F g-1 at a low current density(0.5 A g-1).When increasing to a low current density(5.0 A g-1),the capacitance retention rate was 92.06%.(3)SC-SPI-g-PAM-2 had good applicability and excellent cycle stability,and the electrochemical performance was better than that of a supercapacitor assembled from a commercially available hydrophilic PP/PE composite membrane.(4)After adding KI,the electrochemical performance of supercapacitor had been further improved,the single electrode specific capacitance could reach 365.76 F g-1 at a current density of 0.5 A g-1,which was increased by 150.73%.