Preparation And Performance Studies Of Graphene-based Electrode Materials For Supercapacitors

As an energy storage device,supercapacitor is widely used in power vehicles,rail transportation and other fields because of its high power density and high cycle life,but its energy density severely limits its development.Factors such as the conductivity and void structure of the electrode material affect its energy density in a large extent.As a new type of electrode material,graphene hydrogel has the characteristics of simple preparation,good conductivity and three-dimensional porous network structure.It is expected to be widely used in various supercapacitors.In this paper,the modified Hummers method was used to prepare graphite oxide（GO）,and then three suitable ligand complexing agents were selected to remove the excess manganese ions in GO,and reduced graphene oxide（rGO）was prepared by hydrothermal reduction and hydroiodic acid reduction.After testing,it was found that the various properties of graphene purified by sulfosalicylic acid had been significantly improved.We also used the prepared rGO hydrogel as the cathode material of zinc ion supercapacitor and studied its electrochemical performance.The main contents of this thesis are briefly described as follows:1.Effective removal of manganese in graphene oxide via competitive ligands and the properties of reduced graphene oxide hydrogels and films.We chose citric acid（CA）,tartaric acid（TA）and sulfosalicylic acid（SA）as ligand complexes to effectively remove manganese ions in GO.The results showed that the presence of ligands effectively improved the purification efficiency under the same washing conditions.The manganese content in GO samples was determined to be 0.0083%（GO-CA）,0.0091%（GO-TA）,0.0073%（GO-SA）and 0.025%（GO-HCl）,the manganese content in HrGO-SA is only one third of that without ligand.Subsequent tests showed that the addition of the ligand SA can effectively reduce the manganese content,which shows that the addition of the ligand is an effective way to remove manganese impurities from graphene oxide.2.High-performance Zn-ion hybrid supercapacitors fabricated by using reduced graphene oxide hydrogel as cathode in mixed electrolyte.Here,we use the reduced graphene oxide hydrogel as cathode,the three-dimensional（3D）zinc network electrochemically deposited on carbon cloth as anode and the aqueous solution of zinc sulfate with additive of sodium citrate as an electrolyte to assemble the Zn-ion hybrid supercapacitor.Based on the mass of reduced graphene oxide,high capacitance of 234.3 F g^-1 at scan rate of 1 m V s^-1(or257.3 F g^-1 at current density of 0.1 A g^-1)is obtained.Furthermore,this hybrid device exhibits a superior cycling stability with 85.1%capacitance retention even after 10000charge/discharge cycles at a high current density of 10 A g^-1.This work provides ideas for the design of zinc ion supercapacitors.This dissertation focuses on the preparation of high-quality graphene oxide and its application in zinc ion supercapacitors.Solved the problem of manganese ions impurity removal in graphene oxide and its application in the supercapacitors and preparation of films and planned the development of follow-up work.