All Graphene Electrodes For The High Energy Density Asymmetric Supercapacitor Systems

Human thirst for energy has reached unprecedented levels.In this regard,global interest is in the use of renewable energy,hydrogen,and the development of advanced transportation to reduce concerns about the environment and safety.In order to solve the global energy crisis,we need to develop new energy storage technologies for more efficient use of renewable new energy sources.Supercapacitors(SCs)are widely used as a high power density energy storage device.They can be quickly charged and discharged in a wide voltage window and have a long service life.In order to make full use of supercapacitors as reliable mobile energy sources,it is very important to increase the energy density of supercapacitors at high power densities while designing low-cost,high-performance supercapacitor devices.There is a need to design new electrode materials with high energy density and long life.These electrode materials should have high electrical conductivity and limited structural conformation to provide high specific capacity in a large number of charge and discharge cycles without structural deformation.The electrode has a high specific surface area and a tunable porous structure.It is also very important to promote the surface reaction between the electrode and the electrolyte interface by providing more electrochemically active contact area and accelerating the ion diffusion process.Graphene-based materials have the advantages of large specific surface area,adjustable porous structure,high electronic and thermal conductivity,and can be adjusted by physical and chemical modification methods.They have a wide range of applications in supercapacitors.The main problem of supercapacitors is how to increase the energy density at high power density.Improving the preparation process and technology is an effective way to improve the energy storage capacity of supercapacitors,but in the long run,it is necessary and difficult to find new electrolytes and electrode active materials with high electrochemical performance.The only solution to this problem is to build asymmetric supercapacitors(ASCs).Due to the wider operating voltage window,ASC has a higher energy density than SC.However,a major drawback is the dynamic divergence of the two electrodes,which has yet to be overcome despite recent advances in ASCs.The main reason is the surface activity of the SC electrode,which is usually much faster than the intercalation or redox process of the counter electrode.One of the effective ways to solve the above problems is to adopt a fast surface electrode reaction that can maintain a high energy density at the same time.This work presents a new method for preparing all-graphene asymmetric supercapacitor systems,which solves the problem of electrode imbalance.The main purpose of this paper is to introduce the full surface graphene electrode system by introducing C=O on the surface of r GO and combining it with an iodine-doped graphene(IG)anode to explore the advantages of fast surface reactions of chemically functionalized graphene cathodes.The main purpose of this work is to use the all-graphene electrode system as the counter electrode material,so as to achieve the minimum electrode imbalance and thus obtain high performance.In our work,we introduced the all-graphene ASC system.More specifically,to the best of our knowledge,this is the first report of all graphene ASCs,which compares iodine-doped graphene(IG)anodes with carbonyl-functionalized graphene(FG)cathodes,which has a better performance than previous reports.Compared to ASCs using two electrode materials,this all-graphene electrode system can provide superior performance because both electrodes have the same surface and porous structure,which allows each electrode to work at its maximum capacity.All graphene ASC delivers exceptionally elevated energy and power density values of 91 W h kg^-1 and 424.95 W kg^-1,respectively with 76%retention after 4000cycles.We also designed two graphene-based AMSCs electrode materials,namely functionalized graphene(FG)as a double-layer electrode,and iodine-doped graphene(IG)as a Faraday electrode.Compared with previous MSC systems,this AMSC device has a high specific capacitance,good rate performance,long cycle life,and good energy power distribution,which can be attributed to the use of a full graphene electrode system.The combination of double layer and faradic charge storage in this all graphene based AMSC enables the device to deliver a high energy density(4.75 m Wh cm^-3)and power density(61.55 W cm^-3)with 83%capacitance retention after 5000 cycles.The device also performs very well during the flexibility test for up to 2000 vigorous bending cycles from 0-180^o angle.The performance of this AMSC is better than the previous systems attributable to the synergistic combination of the designed electrodes.In our work,we investigated the dynamics of all-graphene asymmetric micro-supercapacitor systems.We try to design studies in such a way to reveal undiscovered"black boxes"between structure and performance.As mentioned earlier,we have successfully prototyped and obtained the expected results.The main purpose of this research is to find out the electrode imbalance in typical AMSC,and to solve the electrode imbalance problem by using the full graphene electrode system.Two AMSCs were prepared in this project.One is a typical AMSC with Mn O₂ as the anode material and functionalized graphene(FG)as the cathode material,and the other with iodine-doped graphene(IG)as the anode and functional graphite(FG)is a fully graphene AMSC with a cathode.The fabrication of these two devices is compared,showing the difference between a typical AMSC and the new full graphene AMSC we designed.