Fabrication And Properties Of High Performance Paper-Based Supercapacitors With Graphene Electrodes By Laser Engraving

Supercapcitor,also known as an electrochemcal capacitor,is a highly efficient energy storage device.In recent years,with the popularity of portable and wearable devices,micro-flexible supercapacitors have become a hot research direction.Micro-flexible supercapacitors can not only adapt to the portability and foldability of the device,but also have the advantages of high power density and long service life.Therefore,micro-flexible supercapacitors have attracted extensive attention as energy storage devices.Porous fiber paper has the advantages of good flexibility and low price.Especially,its coarse and porous structural features can enhance the adhesion of the electrode material to the paper substrate,facilitate diffusion of electrolyte into the electrode material,thereby promoting charge storage process.Graphene has excellent properties including high electrical conductivity,large specific surface area and high mechanical strength etc.,and thus is widely used as electrode materials in the field of supercapacitors.In this experiment,filter paper was used as the substrate,and electrochemically stripped graphene was used as the electrode material.A high-performance flexible paper-based interdigital supercapacitor was fabricated by laser engraving,whose electrochemical performance was studied.The main results of this work are listed below:(1)A flexible paper-based interdigital supercapacitor was fabricated by laser-engraving patterning method,and electrochemical performance and cyclic stability of the capacitor were tested.The supercapacitor has an area specific capacitance(Cs)of 10.86 mF/cm~2 at a scan rate of 2 mV/s;after 10,000 cycles of charge and discharge test at a scan rate of 50 mV/s,the specific capacitance retention rate is still about 90%,demonstrating that the supercapacitor has excellent charge storage performance and high cyclic stability.(2)Flexibility of the supercapacitor was characterized with galvanostatic charge and discharge(GCD)measurements under the bending degrees of 0,90,180 and a diagonal folding state.The results show that the Cs values under different bending states are almost constant.At the current density of 0.5 mA/cm~2,the supercapacitor has been subjected to the diagonal folding GCD tests for 1000 times and the results show that the area specific capacitance ratio still remains about 98%after the 1000 times folding.These results have indicated that the prepared paper-based supercapacitor in this work has high flexibility.(3)In order to investigate effect of electrode resistance on electrochemical performance of the paper-based supercapacitors,three devices with the same electrode configurations but different electrode resistances(7?/?,20?/?,40?/?)were prepared by laser engraving and performance of the devices were compared.It was found that the electrode resistance is an important factor affecting performance of the supercapacitors.The smaller the electrode resistance,the larger the Cs value and the better rate performance of the capacitor.Among the three studied samples,the supercapacitor with the electrode resistance of 7?/?has the best energy storage performance.The Cs is as high as 9.96 mF/cm~2 at a scan rate of 5 mV/s and8.65 mF/cm~2 at the current density of 0.1 mA/cm~2 respectively,while at the current density of0.6 mA/cm~2,the capacitance retention rate is up to 89.2%,which is higher than the results(76.3%and 80.5%)of the other two capacitors.The results of EIS show that reducing the electrode resistance can reduce the ohmic impedance of the capacitor,promote the ion transport of the electrolyte,and reduce the voltage drop of the capacitor,which is the essential reason for the different electrochemical performance of the three devices.