Preparation Of N-doped Carbon And Amorphous Manganese Oxide And Their Electrochemical Performance

Supercapacitor is an electrochemical energy storage device with simple structure.Compared with secondary cell,it has two outstanding advantages,namely,high power density and long cycle life.It can be widely used in the fields of electronics,transportation and military.The performance of supercapacitor depends largely on the structure and properties of the electrode materials.Therefore,the research of supercapacitor electrode materials has been a focus in the field of electrochemical energy storage.N-doped carbon materials,besides having the advantages of good conductivity and large specific surface area of traditional carbon materials,can also produce Faraday pseudo-capacitor reaction on the surface of carbon materials.Due to synergistic reaction with double-layer capacitors,they have better electrochemical performance than traditional carbon materials.The large surface area and rich pore structure are the basis of the good electrochemical performance of N-doped carbon materials.The traditional carbon material preparation process usually uses a large number of activators to erode carbon skeletons,thereby forming rich pore structure to improve the specific capacitance of carbon materials.However,the highly corrosive activation process is not conducive to the preservation of a large number of nitrogen in carbon materials.Therefore,it is of great significance to develop new technique for the preparation of N-doped carbon materials.Nitrogen doping can effectively improve the specific capacitance of carbon materials.However,the working voltage of the symmetrical supercapacitor assembled by carbon materials is low,resulting in low energy density and inconvenient use.Therefore,an electrode material with a higher specific capacitance is needed.Manganese oxide not only has higher specific capacitance than carbon materials,but also has many advantages,such as abundant reserves,low price,environmental protection and non-toxic.The assembly of manganese oxide and carbon materials into asymmetric supercapacitor can not only enhance the charge storage density of the positive electrode,but also broaden the range of the working voltage of the supercapacitor,thus greatly improving its energy density.Nevertheless,hydrothermal synthesis,solvothermal and electro-deposition methods have been used to prepare high specific surface area manganese oxide materials.There are many problems in these processes,such as tedious process and low preparation efficiency.The purpose of this study is to develop cheap and efficient process technology to prepare carbon and manganese oxide materials with both cost and performance and systematically investigate the electrochemical properties of these materials.The main contents and conclusions are as follows:1.The C₁₀H₁₃K₃N₂O₈ and C₂H₂Cl NaO₂ were used as raw materials to synthesize N-doped porous carbon materials without adding any external activator.The CO₂ and alkali metals produced in the process of carbonization can gently activate carbon materials to form a rich pore structure.At the same time,the nitrogen in the raw material is retained.The nitrogen content in the sample obtained from 700°C carbonization can still be up to 6.54 at%.Electrochemical tests show that,at the current density of 0.5 A·g^-1,the capacitance of the optimum carbon materials can reach to 313 F·g^-1,and at the current density 10 A·g^-1,the specific capacitance retention rate is 73.2%.After30000 charge/discharge cycles,the specific capacity retention rate of the symmetrical supercapacitor composed by it was 119%.2.The manganese oxide electrode materials were prepared by redox reaction of organic agent?PVP;PVA?and KMnO₄ at 250°C.The amorphous and mesoporous structure of manganese oxide effectively improves its conductivity.Moreover,the morphology and agglomeration degree of the particles are regulated by different reducing agents to optimize the electrochemical properties of the products.At the current density of 1 A·g^-1,the maximum specific capacitance of amorphous manganese oxide can reach 451F·g^-1,and the specific capacitance retention rate is 69.8%after 2000 cycles at the current density of 5 A·g^-1.3.In order to verify the feasibility of the preparation process and the electrochemical performance of materials,the above two materials?carbon materials as negative electrode,amorphous manganese oxide as the positive electrode?were assembled as asymmetric supercapacitor.At the work voltage of1.6 V,the specific capacity retention rate is 66.4%after 3000 cycles at the current density of 1 A·g^-1.Considering the simple and low cost of the preparation process,amorphous manganese oxide has potential application value in future supercapacitor storage system.