Studies On Graphene Membrane As Separator In Supercapacitor

Supercapacitor is a new type of electric energy storage device with high power density,long cycle life,maintenance-free,high energy-efficient,fast charging and discharging,fast response,saving energy and environment friendly.And has wide applications prospect by its good performance.Such as the field of electronic devices,electric vehicle industry,aerospace industry,wind power field,solar and LED lights field,rail transportation and so on.Supercapacitor is composed of current collector,electrode,electrolyte and separator.Where the separator is one of the key internal components that requires good electrochemical stability,high porosity and low ion transport resistance.The roles are shown in two aspects: on the one hand,to prevent short circuit caused by the two electrode contact,on the other hand to provide a channel for ions through an electrolyte and constitute ion loop.The performance of separator can directly affect the specific capacity,specific power,equivalent series resistance(ESR),cycle performance and safety performance and many other parameters,one of the pivotal components of the supercapacitor.The graphene material has a unique two-dimensional crystal structure,excellent physical,chemical and thermodynamic properties,which attract wide application areas such as conductive films,lithium batteries,supercapacitors.In this paper,we mainly study the separator of supercapacitors with graphene materials including graphene oxide(GO)and reduced graphene oxide(RGO).The main contents and results are as follows:In the chapter III,GO was synthesized from natural graphite powder by the modified Hummers' method,through vacuum suction prepared into the GO membrane.The morphology of GO separator was analyzed by XRD and SEM,and the electrochemical performance of supercapacitor with GO separator.The morphology observation shows GO separator is thin and the pores form in the GO separator are small slits.Compared to the supercapacitor with PP,the supercapacitor with GO has higher specific capacitance(increased 15.6%),low ESR(2.6? lower),better charge and discharge performance.The use GO film as separator greatly improves the capacitance and energy density of supercapacitor with carbon electrode.This work provides an important reference value for the subsequent research of graphene materials.In the chapter IV,we use the electrochemical method to reduce the GO membrane prepared in chapter III,and obtain the electrochemical reduction of graphene oxide(ERGO),which have a good reduction effect.Research on the properties of electrochemical supercapacitor assembled with ERGO separator,carbon electrode.ERGO has good mechanical properties and thermal stability.The structure,morphology and electrochemical performance were characterized by XRD,SEM and electrochemical workstation.It was found that the ERGO is lamellar interlaced structure,interlayer layer has a larger layer gap(~ 200nm),can serve as a channel for ion diffusion.The better electrochemical performance of supercapacitors with ERGO separator,high specific capacitance(increased 25.6% compared with supercapacitors with PP separator),low resistance,high rate performance,high energy density and good cyclic stability(6.2% attenuation after 2000cycles).This research provides a new high performance separator for supercapacitors.With the rapid development of flexible electronic devices,flexible energy storage devices have also been extensively studied.The research of flexible supercapacitor has also become a hotspot.In Chapter V,we reduced the GO by N2H4 and activated it with KOH to prepare a chemically-reduced graphene oxide(CRGO)electrode material.The ERGO separator described in Chapter IV was assembled into a flexible supercapacitor based on reduced graphene oxide,found that it has a high specific capacitance(186F/g),good flexibility,excellent rate performance and cycle performance(4.8% attenuation after 2000cycles).