The Preparation Of Graphene Film Electrode And Its Electrochemical Performance

With the increasing demand of energy,decreasing reserves of fossil fuel and the aggravation of environmental pollution,New energy which is efficient and clean has become the focus of attention for all over the world.In recent years,The LIBs has the advantages of large energy density,environmental friendly and so on,There is a phenomenon is that domestic and international research focus in the field of power batteries.The electrode material is the key factor affecting the electrochemical performance of lithium ion batteries.Therefore,it is the focus of the present study to prepare high performance electrode materials to improve the energy density,power density and specific capacity of lithium ion batteries.In order to improve the performance of lithium ion batteries,we had prepared the high performance graphene membrane electrodes.The main conclusions are as follows:(1)Graphene oxide was prepared by electrochemical peeling using a salt alcohol method.The graphene surface is not flat and the edge of the slice is more loose,the edge of the layer is also more obvious curl,which is similar to the results of some scholars.The formation of the crimp structure may be that the external force acts on the graphene sheet so that the forces in the plane are unbalanced,resulting in the formation of wrinkles and crimps when the graphene oxide is stripped at the time of mechanical stripping.(2)High performance laminar graphene was prepared by chemical liquid reduction with KOH as reducing agent.The laminar graphene has a layered polycellular structure and a high specific surface area(428.3 m2g-1).At the same time,the abundant porous structure of laminar graphene were verified in nitrogen adsorption and desorption experiments,and it had a large number of microporous(1.2 nm)and macroporous(80 nm)structures.It is shown that the graphene has a porous structure after treatment with KOH,and the distance of these porous structures is much larger than the radius of lithium ions(r(Li+)= 0.076 nm).This layered polycellular structures are conducive not only to the intercalation and deintercalation of lithium ions during the charging and discharging process,but also can increase the number of lithium storage points,so that the lithium ion battery have higher reversible specific capacity,faster charging cycle,more power storage.(3)Graphene membrane electrode was prepared by coating the graphene slurry on the copper foil current collector by coating method.0.5 g actived graphene was dissolved in 10 mL of deionized water and ultrasonically pulverized by ultrasonic cell pulverizer for 90 min to disperse the activated graphene in solution.Mixed the PVDF and NMP(N-methyl pyrrolidone,do not need to heat up,the temperature may cause NMP volatile),added conductive agent after the PVDF dissolved(about 1 h or so),and then added conductive agent dispersed evenly(1 h)to the ultrasonic crushing of graphene solution.Finally added the appropriate amount of NMP to adjust the viscosity,then mixed the two solutions to get the electrode slurry.Copper foil as a negative electrode material,the first thing is pretreatment of copper foil.Removing the oxide layer on the surface of the copper foil,improving the surface smoothness of the copper foil,increasing the the adhesion stability.A graphene thin film was coated on the copper foil by a coating method which is a graphene membrane electrode.(4)Electrochemical performance of the graphene membrane electrode was tested by BTSDA battery detection system and Metrohm Autolab electrochemical workstation.The results show that the contact resistance of the graphene membrane electrode(K/Graphene-ME)after KOH treatment is smaller than Graphene-ME which is not treat with KOH.This result is favorable for the recharging and discharging cycle,the conductivity of the graphene membrane electrode can be maintained,and improved the electron transfer reaction rate in the process of embedding and deintercalation of lithium ions in charge and discharge process.The initial discharge and charge reversible specific capacity of the graphene membrane electrode can be 1138 mAh g-1 and 831 mAh g-1.The graphene membrane electrode was tested for 10 cycles at the current density of 100 mA g-1,the reversible specific capacity of the graphene membrane electrode can be 788.4 mA g-1.When the current density is as high as 3000 mA g-1,the reversible specific capacity of the graphene membrane electrode can still reach 386.8 mAh g-1.After the lithium ion battery was cycled 1000 times,the capacity can still be maintained at about 99.7%,which indicates that the excellent cycling performance of the graphene membrane electrode which is related to the high specific surface area,the layered polycellular structure and the low charge transfer resistance of the graphene.