Design And Performance Study Of Flexible Supercapacitor

With the rapid development of flexible electronic devices,it is necessary to develop a matching flexible energy storage system.Flexible supercapacitors are an important part of flexible energy storage system due to their advantages of long life,no pollution,safety and risk,and good mechanical properties.In this paper,the research progress of supercapacitors is introduced,and the research status of flexible substrate and electrode materials is reviewed.Focusing on the flexible supercapacitor materials and devices with high performance,a series of researches have been carried out in this paper,including the preparation of composite materials,the design of electrode structure and the device assembly strategy.In view of the phenomenon that the active material falls off in the process of mechanical deformation,the in-situ growth and calcination are used to strengthen the binding force between the active material and the substrate.Through homogeneous carbon doping,the electrical conductivity and electrochemical stability of the material are improved.In this paper,a new type of linear flexible electrode structure is designed,and a safe and non-toxic packaging material is used to fabricate a linear flexible supercapacitor,which can resist the structural and functional failure caused by deformation.Graphene-metal oxide composites are prepared by laser direct writing technology to process polyimide films.A simple,easy to operate,high efficiency and environmentally friendly process for the preparation and packaging of flexible microcapacitors is developed.The main research contents and conclusions are as follows:(1)Homogeneous carbon doping can effectively inhibit the volume effect of electrode materials in the process of charge and discharge,and achieve excellent electrochemical stability.In this paper,MOF-5 is used as the precursor,and the rod-shaped carbon composite Co₃O₄ array composed of small grains is prepared by calcination,enhancing the infiltration between electrolyte and electrode material,with increased electrolyte ion channels and reduced ion diffusion distance.Thus,the material shows excellent charge storage ability.The study of electrochemical kinetics and energy storage mechanism shows that the contribution of electrochemical double layer capacitances(EDLCs)gradually increases with the increase of scanning rate.At the current density of 1 m A/cm²,the capacitance of electrode materials is calculated as 3.17F/cm².More importantly,at a scanning rate of 50 m V/s,the capacitance remains 96.7%of the initial value after 20000 life cycle tests.In addition,the assembled symmetrical solid-state supercapacitors show good flexibility and wide operating voltage range,achieving high power and high energy output.(2)Carbon cloth(CC)has good electrical conductivity and mechanical flexibility,so it is an ideal substrate for flexible supercapacitor.Compared with Co element,Mn element is more abundant in the crust and its price is lower.Mn₃O₄/PPy is grown on the surface of CC by electrodeposition.After simple calcination,Mn₃O₄@CC nanowire electrode is obtained,and the electrochemical area of electrode of per square centimeter is up to 2187 cm².Under the condition of 0.5 m A/cm²,the area capacitance of Mn₃O₄@CC electrode reaches 1094.1 m F/cm².Star-like Mn S is prepared by hydrothermal vulcanization method,which enhanced the charge storage capacity of the electrode material.Because S is more electronegative than O,its metal compounds have higher electrical activity.Under the condition of 1 m A/cm²,the area capacitance of Mn S@CC is as high as 2171.8 m F/cm².At the high current density of 8 m A/cm²,it still keeps 608.8 m F/cm².The assembled symmetrical solid-state supercapacitors can work normally in the bending condition,and the performance does not decay,demonstrating excellent mechanical flexibility.(3)The linear electronic devices have the remarkable advantages of ultra-thin,lightweight,strong flexibility,and can withstand serious mechanical deformation.What's more,the wire-like capacitors can be easily integrated into textiles and fabrics through traditional weaving techniques for wearable applications.Therefore,three kinds of linear flexible electrodes were prepared in this paper,including PPy-C@CC electrode derived from the carbonized polypyrrole(PPy),Mn₃O₄/PPy electrode and the electrode based on graphene and Polydimethylsiloxane(PDMS).Their electrochemical test are carried out to show good charge storage ability.The linear asymmetric flexible solid supercapacitors with parallel and coaxial structures are assembled by selecting flexible electrodes and solid electrolyte,which showed good electrochemical performance and excellent mechanical flexibility.They could be programmed into clothing as the energy of flexible electronic devices.Three linear flexible supercapacitors in series can light up green LED lights.(4)After being heated by a transient laser,the PI film surface is transformed into a porous graphene network(also known as laser-induced graphene,LG),which has good physical and electrical properties and is suitable for the preparation of miniature supercapacitors.In this paper,Ni Co₂O₄ is grown in situ on the surface of LG by electrodeposition to realize the fabrication of planar micro-graphene flexible electrode.The electrochemical performance of the electrode is the best when the electrodeposition time is 600 s,and the area capacitance of the electrode reaches 30.2 m F/cm² when the current density is 0.1 m A/cm².In addition,in order to simplify the processing procedure,nickel nitrate is uniformly dispersed in PI,and the uniform Ni Ox@LG electrode is prepared by laser induction in one-step.Then,a planar cross-finger solid supercapacitor is assembled using solid electrolyte and PDMS.The packaged device has excellent mechanical flexibility and can be integrated into a flexible electronic device to directly contact the human skin.