Preparation And Energy Stroage Properties Of Hierarchical Porous Nitrogen-doped Carbon And Carbon-based Composite Materials

With the rapid development of modern society,people’s demand for various electronic products is also increasing,so the research on high-performance energy storage and conversion equipment has become the focus.Supercapacitors have received widespread attention due to their high cycle stability and fast charging/discharging capabilities.Carbon materials are considered to be the ideal choice for energy storage electrode materials due to their good electrical conductivity,adjustable pore structure and excellent thermal stability.In order to further improve the electrochemical performance of carbon materials,it can be doped with heteroatoms or compounded with pseudocapacitive materials.Based on the above ideas:in this thesis,carbon-based electrode materials with hierarchical porous structure are the main research contents.Firstly,hierarchical porous graphitized carbon nitride with high nitrogen content was successfully prepared by using double nitrogen-containing precursors and adjusting the amount of pore-forming agent.Subsequently,hierarchical porous nitrogen-doped carbon materials with adjustable pore structure were prepared by improved non-solvent induced phase separation method and template method.Finally,polyaniline,a conductive polymer material with excellent pseudocapacitive properties,was grown on carbon cloth.Flower-like polyaniline was effectively loaded by multiple depositions,and a high-performance carbon cloth/polyaniline flexible electrode material was obtained.The specific research contents are as follows:（1）Preparation of porous graphitized carbon and nitrogen with 3 D interconnected network structure and its energy storage properties.Graphitized carbon nitride materials with hierarchical porous structure were prepared by one-step calcination method using ammonium bicarbonate as pore-forming agent,urea and melamine as double nitrogen source and sacrificial template precursor.During the calcination process,the gas produced by the high temperature decomposition of ammonium bicarbonate acts on the nanosheet template formed by the precursor,forming a pore structure,effectively alleviating the stacking phenomenon of the product sheet,and forming an interconnected three-dimensional network structure.Based on the above structural characteristics,the product exhibits excellent electrochemical performance:in the three-electrode system,the specific capacitance can reach 520 F g^-1at a small current density of 0.1 A g^-1.When the current density increases to 20 A g^-1,the specific capacitance can still reach 219.4 F g^-1.After 10000 charge-discharge cycle tests,the capacitance retention rate can reach104.1%,showing excellent cycle stability.When assembled with ionic liquid EMIBF₄as electrolyte,it can provide an energy density of 28.49 Wh Kg^-1at 662.56W Kg^-1.The improved porous structure and composition make the product exhibit excellent energy storage properties in the test,which is expected to be applied as a high-performance electrode material.（2）Preparation of three-dimensional graded porous nitrogen-doped carbon materials by non-solvent induced phase separation and their energy storage properties.Using polyacrylonitrile（PAN）,graphene oxide and porous ZIF-8（P-ZIF-8）as raw materials,the three-dimensional macroporous structure was formed in the PAN membrane by the non-solvent induced phase separation process and the structural induction effect of graphene oxide.The macroporous structure of the product was retained by high temperature calcination.At the same time,P-ZIF-8 was calcined to form nitrogen-doped carbon material particles with mesoporous structure,which were dispersed in the product matrix to form a hierarchical porous structure.The above structure makes the product have a high specific surface area of 224.64 m²g^-1.In the three-electrode system,the specific capacitance of the product PG-ZC₅₀is 499.7 F g^-1at 0.1 A g^-1.At 20 A g^-1,the specific capacitance can still reach 179.6 F g^-1.In addition,PG-PZC₅₀showed excellent cycle stability,and the specific capacitance did not decrease after 10,000 GCD cycles.When assembled into a symmetric supercapacitor,the supercapacitor can exhibit a maximum energy density of 6.23 Wh Kg^-1at 258.89 W Kg^-1.The superior electrochemical performance of PG-PZC₅₀indicates that it is an effective method to improve the energy storage properties of electrode materials by regulating the hierarchical porous structure of the product through structure induction effect and non-solvent phase separation method.（3）Preparation and energy storage properties of flower-like polyaniline nanosheet clusters/carbon cloth composite electrode materials.Using carbon cloth as conductive substrate and polyaniline as pseudocapacitive material,a flower-like material stacked by polyaniline nanosheets was grown on carbon cloth by repeated deposition.The affinity between the pre-loaded polyaniline and the new aniline monomer plays a decisive role in the formation of products with sheet morphology.The flower-like structure formed by nanosheet assembly has a larger specific surface area and more pores for electrolyte ion adsorption,migration and storage.At the same time,the structure can also expose more active sites to the product,which is conducive to the redox reaction during charge and discharge.Benefiting from the reasonable morphology and composition ratio,the composite material exhibits excellent energy storage properties:Benefiting from the reasonable morphology and composition ratio,the composite material exhibits excellent energy storage properties:The specific capacitance reaches 1421.9 m F cm^-2at 1 m A cm^-2.After 5000 cycles of charge/discharge in the two-electrode system,the capacitance retention rate can reach68.75%;when the surface power density is 249.7μW cm^-2,the maximum surface energy density of the capacitor is 33.5μWh cm^-2.In this study,a composite material with an optimized lamellar structure of PANI grown on a flexible substrate was constructed,and a synthesis strategy for effectively forming a lamellar PANI on the substrate was proposed.This method is expected to obtain more diversified high-performance electrode materials.