Preparation And Doping Modification Of Lignite-based Porous Carbon For Supercapacitors

Supercapacitor is a new energy storage device with the advantages of high power density,long cycle life and environmental-friendness.Coal-based porous carbon can be used as electrode materials,and China is rich in coal,coal-based activated carbon is of potential for supercapacitor electrode.In this thesis,Baoqing lignite was used as raw material,extracted by K₂CO₃solution,the extracted solution was centrifuged,dried,hydrothermally treated and activated to obtain lignite-based porous carbon.SEM,XRD,XPS,and N₂ adsorption and desorption tests were used to study the structure,morphology of porous carbon.GCD,CV,and EIS were used to study the electrochemical properties of porous carbon.Through the orthogonal test design,it was determined that the activation temperature has the greatest influence on the electrochemical properties of the porous carbon.The porous carbon produced by the better preparation conditions derived from the orthogonal test had the highest specific capacitance,293 F g^-1 at 1 A g^-1,and the specific capacitance was 134 F g^-1 when the current density increased to 10 A g^-1.The specific capacitance retention of the cell after 10000 cycles was 113.4%,and the better conditions with the better electrochemical performance.Nitrogen doping can effectively improve the electrochemical performance of porous carbon.Hydrothermal nitrogen doping is efficient and simple.On the basis of the previous research,nitrogen-containing reagent were added in the hydrothermal process to prepare nitrogen-doped porous carbon.When urea was used as nitrogen source,the optimal urea addition was 2.4 wt.%,activation temperature was 700 ^oC.The specific capacitance of the N-doped porous carbon was 305.1 F g^-1 at 1 A g^-1,221 F g^-1at 10 A g^-1.The energy density of the coin-cell reached 5.86 Wh kg^-1 at 500 W kg^-1 and remained 4.58 Wh kg^-1 if power density was 5000 W kg^-1.The specific capacitance retention was 107.4%after 20000 cycles.When NH₄Cl was used as nitrogen source,the better NH₄Cl addition was 8 wt.%,activation temperature was 800 ^oC.The specific capacitance of N-doped porous carbon was 282 F g^-1 at 1 A g^-1,178 F g^-1 at 10 A g^-1.The cell achieved an energy density of 6.35 Wh kg^-1 at 500 W kg^-1,and an energy density of 4.58 Wh kg^-1at 5000 W kg^-1.The specific capacitance retention was 104.4%after 20000 cycles.When melamine was used as nitrogen source,the better melamine addition were 6 wt.%,activation temperature was 700 ^oC.The specific capacitance of the N-doped porous carbon was 320.9 F g^-1 at 1 A g^-1,206 F g^-1 at 10 A g^-1.The cell achieved an energy density of 7.32 Wh kg^-1 at 500 W kg^-1,and an energy density of5.69 Wh kg^-1at 5000 W kg^-1.The nitrogen-doped porous carbon has excellent electrochemical properties,which can be explored for the high value-added utilization of low-value lignite.There are 83 figures,21 tables and 131 references in this thesis.