Preparation And Supercapacitor Property Of B And N Co-doped Carbon Microspheres

As a new type of energy storage device,supercapacitors have received widespread attention owing to their high power density,fast charge–discharge performance,and long cycling life.However,their low energy density and high production costs have restricted their commercial applications.As an important part of supercapacitors,electrode materials are considered to be the key to restricting their performance.The development of simple synthesis strategies to prepare electrode materials with high energy density has become an urgent problem to be solved.This paper proposes to use the spray drying method to prepare boron-nitrogen co-doped carbon microspheres electrode materials.By doping boron and nitrogen elements,constructing porous structures and optimizing electrode structure,the specific surface area of the material was increased,and the ion transmission inside the electrode was optimized.These approaches have realized the improvement of the capacitance performance,rate performance of electrode materials and the energy density of supercapacitors.The main research contents of the thesis are as follows:（1）Using glucose,melamine and boric acid as carbon precursors and dopants,the boron nitrogen co-doped carbon microsphere materials were prepared by spray drying method.The effect of pyrolysis temperature on the doping content of heteroatoms was investigated.Research has found that the spray drying process can achieve uniform mixing of reagents at the molecular level,ensuring uniform doping of boron and nitrogen elements.As the pyrolysis temperature increases,the amount of nitrogen doped in the sample decreases,and the degree of graphitization of the carbon material increases.Heteroatom doping can improve electrode wettability and provide pseudocapacitance,while graphitic carbon can improve electrode conductivity and reduce internal resistance.Through testing,it is found that the sample pyrolyzed at 800℃for 2 h has a suitable degree of graphitization and a higher content of heteroatom doping（wherein,nitrogen and boron content are 12.4at%and 3.2at%,respectively）,so BNCs-800 Shows the best capacitance performance(the specific capacitance is 218.5 F g^-1at a current density of 1 A g^-1).However,due to the single pore structure of the material,the diffusion of ions is hindered and the capacitance retention rate during high-speed charging and discharging is affected.（2）Using Na Cl as a template,a salt-assisted spray drying method was used to prepare porous carbon microspheres co-doped with boron and nitrogen.The influence of Na Cl concentration in the precursor solution on the microstructure and electrochemical performance of the material was investigated.The study found that the Na Cl template can effectively introduce the porous structure into the material,and the pore structure and specific surface area of the material can be adjusted by adjusting the Na Cl concentration.As the concentration of Na Cl increases,the pore size of the sample gradually increases,and the specific surface area first increases and then decreases.Among them,the sample prepared under the condition of Na Cl concentration of 4 g L^-1 has the highest specific surface area(1848 m2 g^-1).The high specific surface area provides sufficient active sites for ion adsorption,so the sample shows a high specific capacitance of 472.6 F g^-1 at a current density of 1 A g^-1.In addition,the rich hierarchical porous structure improves the electrolyte diffusion and ion transfer efficiency.The assembled symmetrical supercapacitor show a specific capacitance of 360.8 F g^-1 at a current density of 0.2 A g^-1,and an energy density of 13.2 Wh kg^-1 at the power density of 500 W kg^-1.The capacitance retention rate is about 94.5%after 10,000 cycles.（3）In-situ deposition of boron-nitrogen co-doped porous carbon microspheres on a carbon cloth substrate by spray drying technology to prepare a three-dimensional flexible electrode material.There is no need to add conductive materials and binders during the preparation process,the electrode material has excellent specific capacitance(when the current density is0.5 m A cm^-2,the specific capacitance is 802 m F cm^-2)and long cycle life（after 2000 cycles,the post-capacitance retention rate is 96.2%）.