Preparation Of PVA Based Gel Electrolytes And Design Of Flexible Integrated Supercapacitors

The flexible supercapacitor composed of gel electrolyte has the characteristics of lightness,low cost,high flexibility and so on,which therefore could be used as energy devices of wearable and portable electronic instruments,so it may have pretty promising application prospects.Generally,flexible supercapacitors exhibit a multi-layer laminated configuration,which is composed of solid electrodes and gel electrolyte in between.On account of this multi-layer laminated configuration,the Interface contact resistance will be increased,which will reduce the efficiency of transmission from cathode to anode in supercapacitor charge and ions.Nevertheless,the unavoidable relative displacement among the multi-layers during the consecutive bending or stretching cycles may cause delamination of these multilayers,which will undoubtedly decrease the device performance.In this paper,highly flexible and free-standing gel electrolytes were prepared by chemical crosslinking and freezing thawing methods.The polymer electrode materials were in-situ polymerizated on the surface of those gels,so that the electrode materials and the flexible electrolyte were tightly bonded to form an integrated and flexible supercapacitor,which greatly reduc the contact resistance between the electrode material and the electrolyte,thereby enhancing the electrochemical performance of flexible supercapacitors.The main contents of this paper include the following aspects:?1?Flexible free-standing PVA/PEG gel electrolytes were prepared by chemical crosslinking with sulfuric acid as a catalyst and proton source.By controlling the mass ratio of polyethylene glycol to polyvinyl alcohol,PVA/PEG gel electrolytes with regular cross-sectional morphology and regular porous skeleton structure was prepared.Its ionic conductivity reached 67.1 mS/cm,the maximum stress reached36.4 kPa.The gel electrolyte and carbon cloth were assembled into flexible supercapacitors and tested by electrochemical method.The area-specific capacitance was 31.44 mF/cm² at a current density of 0.2 mA/cm²,and the specific capacitance remained unchanged after 10000 cycles of charge discharge.?2?PPy-PVA/PEG films were prepared by in-situ polymerization of polypyrrole electrode materials on the surface of free-standing PVA/PEG gel electrolyte by chemical in-situ polymerization.By controlling the concentration of pyrrole monomer during polymerization,PPy-PVA/PEG films with spherical surface morphology were prepared and assembled into flexible supercapacitors.The area-specific capacitance reaches 216 mF/cm² at a current density of 0.2 mA/cm².The energy density of the device reaches 7.49?Wh/cm² at the power density of 200?W/cm².2000 cycles of constant current charge discharge at a current density of 1 mA/cm² can maintain 57.9%capacitance.?3?Poly?Ani-co-Py?-PVA/PEG films were prepared by in-situ polymerization of copolymers of pyrrole and aniline on the surface of free-standing PVA/PEG gel electrolyte.By controlling the molar ratio of pyrrole monomer to aniline monomer during polymerization,the Poly?Ani-co-Py?-PVA/PEG films with excellent electrochemical properties were prepared and assembled into flexible supercapacitors.The area-specific capacitance reaches 772.8 mF/cm² at a current density of 0.2mA/cm².The energy density of the device reaches 26.83?Wh/cm² at the power density of 200?W/cm².2000 cycles of constant current charge discharge at a current density of 1 mA/cm² can maintain 85.99%capacitance.The bending test of supercapacitor shows that the specific capacitance is almost unchanged under different bending conditions,and it can still keep 95.85%after 1000 bending cycles.?4?PVA-H₂SO₄ gel electrolytes with self-healing function were prepared by freezing and thawing with sulfuric acid as the proton source.The self-healing PVA-H₂SO₄ gel electrolytes with good electrochemical performance were prepared by controlling the concentration of sulfuric acid.Its ionic conductivity was 101.23mS/cm.The Poly?Ani-co-Py?-PVA film was prepared by in-situ polymerization of copolymers of pyrrole and aniline on the surface of the gel.After being assembled into a super capacitor,electrochemical tests were carried out.The area-specific capacitance reaches 544 mF/cm² at a current density of 0.2 mA/cm².The energy density of the device reaches 18.89?Wh/cm² at the power density of 200?W/cm².The specific capacitance of the supercapacitor increases first and then decreases after cycling.The capacitance retention rate is 178.82%at 4700 cycles and 11.76%at10000 cycles,the capacitance retention rate recovered to 88.24%after 2 days at room temperature.