Preparation And Performance Of All-solid Flexible Supercapacitors Based On Ionic Liquids /Polymers

The rapid development of portable and wearable electronic devices is leading flexible energy storage devices with light weight,small size,high energy density and power density to be the main attention of current research.Flexible solid-state supercapacitors are considered as one competitive energy storage device due to the advantages of fast charge and discharge speed,high cycle stability,high safety,and good electrochemical performance under different deformations.The performance of capacitors depends on the materials and properties of their core components(electrodes and electrolytes).At present,most of the flexible solid supercapacitors use carbon material as the electrode,but the electrochemical performance of carbon electrode is greatly affected by the specific surface area and pore size distribution,and the mechanical properties of supercapacitors based on carbon electrode need to be improved.However,flexible all-solid supercapacitors,which are assembled by electrodes and electrolytes based on polymers,show particularly outstanding advantages in this field.In recent years,the relevant reports have been limited,and there is a very large research space in this field.In order to obtain flexible all-solid polymer supercapacitors with excellent electrochemical and mechanical properties,the present paper designed and synthesized polymer film electrodes with excellent mechanical properties(PANI/ILn/PVA)using composite films of polyvinyl alcohol(PVA)and ionic liquid(IL),which were used as the substrates of polyaniline(PANI)generated through chemical oxidation in-suit polymerization.The optimal polymer electrodes were chosen through studying the electrochemical,mechanical and thermal properties of PANI/ILn/PVA polymer electrodes with different IL contents.After that we studied the electrochemical properties under different deformation conditions.And then,PVA/H₂SO₄/IL gel was used as the gel electrolyte to assemble a symmetrical polymer supercapacitor with the prepared flexible electrodes.Finally,we studied the electrochemical performance and the effect of deformation on it.Firstly,the ILn/PVA composite film prepared by freezing-thawing cycles was used the flexible substrate,and then the PANI/ILn/PVA flexible polymer electrode is in situ polymerized through chemical oxidation.The effect of IL content on the polymer electrode performance was studied,and the results show that the introduce of IL is helpful for the enhancement of conductivity and mechanical properties of electrode materials.The PANI/IL₁₀₀/PVA polymer electrode had the best comprehensive performance when the IL content is 100%of the mass of PVA.At 1 mA/cm²,its area specific capacitance and conductivity were 266.6 mF/cm² and 6.49S/m,respectively.The capacitance retention rate was 93.8%after 1000 times constant current charge-discharge cycles.The polymer electrode has outstanding mechanical properties,the tensile strength was 1.27 MPa,and the elongation at break could reached 509.19%.In addition,the flexibility test results showed that the PANI/IL₁₀₀/PVA flexible polymer electrode could work normally after being bent at 180°for 200 times with capacitance retention of 86.4%.On the basis of the above research,we assembled the flexible all-solid polymer supercapacitors using carbon cloth,PANI/IL₁₀₀/PVA and PVA/H₂SO₄/IL as collector,electrode and gel electrolyte,respectively.The effect of IL content in gel electrolyte on the electrochemical performance of supercapacitor was studied and the results show that the flexible all-solid supercapacitors had optimal electrochemical performance when the IL content in the gel electrolyte is 100%of the mass of PVA.The area specific capacitance is 251.2 mF/cm²at 1 mA/cm²,and the capacitance retention kept 77.2%after 1000 cycles of constant current charge-discharge cycles.It has high energy density of 34.9?Wh/cm² with 610.4?W/cm²of power density,reaching an energy density of 10.3?Wh/cm² at a high-power density of 1972.3?W/cm².In addition,the flexibility test results showed that the all-solid polymer supercapacitor could still keep excellent electrochemical performance under different bending angles,indicating the great potential applications in portable and wearable electronic devices.