Printed Flexible Supercapacitors Based On Carbon Materials

At present,technological progress in wearable electronics,green energy and other fields is often limited by the lack of energy storage devices.Supercapacitors are the most attractive solution to meet the needs of these fields in energy supply,service life,stability,quick charge and discharge,flexibility and safety.Supercapacitors have high energy density,power density,cycle life and stability,in addition,they also have the characteristics of fast charging and discharging and safety,which are incomparable to other energy storage devices.In this paper,carbon material and supercapacitor are used as the research object,and the construction of supercapacitor electrode is realized by means of printing electronic technology to improve the energy storage performance of supercapacitor.The research contents and conclusions of this paper were summarized as follows:（1）Graphene oxide（GO）was compounded with silver nitrate by electrostatic adsorption,and then printed with aqueous solution of silver nitrate into a film.Last,RGO/Ag composite was prepared by gas phase reduction.The influence of preparation technology on the composites with conductivity was studied,the structure and properties of composites were analyzed and characterized.It was found that the generated silver particles with 5nm were inserted into the graphene sheets,preventing the agglomeration of graphene and increasing its conductivity,so that conductivity of the composite material could reach up to 2.9×10⁵ S/m.In addition,application of the vapor phase reduction method and the silver particles have synergized to generate a porous channel inside the prepared RGO/Ag composite,which gives the composite excellent electrochemical properties with an area ratio capacitance of 60.6 m F/cm².Furthermore,the RGO/silver conductive film showed excellent flexibility.The square resistance hardly changed at the bending time of 0～180°,and the square resistance rate remained within 0.1 at the bending time of less than 150 times.（2）Using ink-jet printing technology,an aqueous solution with a mass ratio of 1:3 between GO and silver nitrate was used as ink.Supercapacitor electrodes with three-dimensional structure were prepared by stacking ink layers and by vapor phase reduction with hydrazine hydrate.The results show that when the printing temperature is not less than 55℃and the printing interval is not less than 40s,the ink has good drying effect and could print uniform electrode.According to the test results,the three-dimensional electrode was mainly based on the energy storage effect of double layer,and had good reversibility of charge and discharge.Moreover,the three-dimensional structure makes the electrode area 3.4 times higher than the capacitance.At the scanning rate of 5m V/s,the area-to-capacitance of 209 m F/cm²could be reached.Even at the scanning rate of 50 m V/s,the area-to-capacitance of the electrode could reach 99.5 m F/cm².The area-capacitance retention rate could reach47.6%,and the three-dimensional electrode has good multiplier performance.In addition,it was found in the ac impedance test that the three-dimensional structure was favorable for electrolyte ions to diffuse to the electrode surface.The three-dimensional electrode showed ideal capacitance characteristics.（3）On the basis of printing 3D electrode,the flexible supercapacitor was assembled with 1 mol/L H₂SO₄/PVA gel as electrolyte,and its performances such as capacitance,ratio,flexibility,cycle life,power density and energy density were tested and analyzed.It was found that the assembled flexible supercapacitor could achieve the area-specific capacitance of up to 186.42 m F/cm²,even at the scanning rate of 10 times,the capacitance retention rate was still as high as 63.8%.The assembled supercapacitors have an energy density of up to 2.59 Wh/L and a power density of up to 1.39 k W/L,better than some commercial supercapacitors.In addition,the assembled supercapacitor showed good flexibility,excellent cycle life and cycle stability.After2000 cycle tests,the capacitance retention rate of the assembled supercapacitor could reach 87.3%.In summary,graphene and silver were assembled together by electrostatic adsorption and vapor phase reduction method,preventing the aggregation of graphene,and porous channels were formed in the RGO/Ag nano composites,resulting in excellent conductivity and electrochemical properties of the composites.In addition,3D electrodes were prepared by printing based on graphene/nano-silver composites.The three-dimensional electrode was assembled into a flexible supercapacitor through a gel electrolyte.The supercapacitor showed excellent electrochemical performance,flexibility and cycle life,as well as good power density and energy density,which is very suitable for the storage device of small electronic devices.