Preparation Of Multifunctional Gel Polymer Electrolyte And Its Application In Flexible Supercapacitors

Supercapacitors（SC）are regarded as one of the most promising energy storage devices in the 21st century due to their fast charging and discharging speed,long cycle life,high power density and good operation safety.Electrolytes are one of crucial factors for achieving high performance of SCs.Gel polymer electrolyte（GPE）has the advantages of wide operating voltage range and relatively stable system,which solves the shortcomings of liquid electrolytes and solid electrolytes.As a new type of energy storage device,SCs assembled with GPE generally have good cycle stability and safety performance,and have broad application prospects in the field of thin and light electronic devices and flexible energy storage devices.However,under the physical effects of bending,shearing and stretching,the flexible wearable electronic products may lead to device failure or even serious safety problems.Therefore,it is imperative to design a GPE that can repair itself when external forces are applied.In addition,in the traditional water system,GPE inevitably freezes at low temperature,restricting ion transmission and causing the device to stop working.It’s necessary to study the effect of temperature on the ions conductivity of GPE at low temperature by adding acid/salt electrolyte to reduce freezing point.At present,there is still some distance between the research and practical application of GPE in SC.This thesis is mainly about the water system GPE,including polyacrylamide（PAM）-polyvinylpyrrolidone（PVP）-H₃PO₄,polyvinyl alcohol（PVA）-tannic acid（TA）-H₃PO₄,and PVA-sodium alginate（SA）-Fe³⁺-Na₂SO₄GPEs.The performances of the electrolytes and the electrochemical properties of the SCs were investigated.The details are as follows:1.In System 1,PAM-PVP-H₃PO₄semi-IPN GPE was prepared by chemical cross-linking.The effects of different PVP contents and H₃PO₄concentrations on GPE and SC properties were studied by electrochemical,mechanical measurements and structural characterizations.The experimental results show that semi-IPN effectively enhances the mechanical properties of GPE.Under optimal conditions,the prepared GPE has not only excellent tensile properties(the elongation at break of 17.42mm·mm^-1),but also high flexibility（knotting and twisting）.Meanwhile,owing to its interconnected 3D porous network structure,it provides abundant channels for ion migration,which brings the GPE for good ionic conductivity(0.138 S·cm^-1).Besides,the GPE displays a good ionic conductivity during the low temperature test.SCs assembled with the GPE have excellent electrochemical performances,including good electrode specific capacitance and excellent electrochemical stability.In addition,a large tensile strain up to 100%and a high bending angle of 230^oare achieved with good capacitance retention.Even at-40°C,SC still has excellent electrochemical performances and mechanical flexibility.2.Since system 1 adopts chemical cross-linking method without self-healable property,system 2 adopts freeze-thaw method and soaking method to prepare fully physical cross-linking multifunctional supramolecular PVA-TA-H₃PO₄GPE.The effects of different TA contents and H₃PO₄concentrations on GPE and SC properties were studied.The experimental results show that the prepared multifunctional supramolecular GPE has excellent self-healing property.Multifunctional supramolecular synergy endows the GPE good flexibility and high stretchability(the elongation at break of 18.34 mm·mm^-1),meanwhile,it inhibits the formation of PVA crystallites and makes the amorphous phase of GPE increase,which is beneficial to the ionic conductivity(0.02 S·cm^-1).The multiple hydrogen bonds of PVA-TA and PVA networks lead to fascinating self-healable properties.SC assembled with the GPE is able to recover its configuration,mechanical and electrochemical properties autonomously within 10 min without external stimulus,and the cutting-healing cycles can be repeated for at least 10 times.3.SC has high power density,but its energy density is relatively low.In system 3,PVA-SA-Fe³⁺-Na₂SO₄interpenetrating network（IPN）GPE was prepared by inducing the pseudo-potential effect of the redox active electrolyte to increase the capacitance of the SC.The effects of different SA contents and Fe³⁺concentrations on GPE and SC properties were studied.Addition of SA can form a semi-IPN structure with PVA to makes the cross-linked network more complete,better disperse and transfer stress,and enables GPE have good flexibility and high stretchability(the elongation at break of 6.61 mm·mm^-1).At the same time,because of its 3D porous network structure,GPE has good ionic conductivity(0.082 S·cm^-1).Cyclic voltammetry displays the redox peak of Fe³⁺appears,which indicates that a redox reaction occurs,and the hydrogen bonds formed between PVA and SA make GPE self-healing.The GCD curve of SC shows the pseudocapacitance from redox reaction.It is found that the capacitance value is increased by 116.6%(with current density of 150 m A·g^-1)compared to that without Fe³⁺.Moreover,the SC still has good electrochemical stability under low temperature and bending deformation conditions.