Preparation And Electrochemical Performance Of Phenolic-based Carbon Spheres And Nitrogen-doped Porous Graphitized Carbon Spheres

As a new type of energy storage device,supercapacitors have longer cycle life and faster charging and discharging speeds than traditional energy storage devices.Phenolic-based carbon spheres have been widely studied in the field of supercapacitor electrode materials due to their controllable structure,high degree of customization,and the same developed three-dimensional network structure,as well as higher packing density.In this experiment,resorcinol and formaldehyde were used as carbon sources,and the St?ber method was used to hydrothermally synthesize resorcinol-formaldehyde-based carbon balls(RFC)with a microstructure and a controllable particle size,It not only shortens the experiment cycle,but also saves energy while ensuring the safety of the experiment,and draws the best preparation plan based on the reaction conditions.Based on this,graphitized carbon spheres are obtained by Ni low-temperature catalytic graphitization,and the experimental process for the best catalytic graphitization effect is determined according to the experimental plan,and the catalytic graphitization mechanism is analyzed.Afterwards,a one-pot method was used to successfully prepare nitrogen-doped porous graphitized carbon spheres.Melamine was used as the nitrogen source and before heat treatment,NiCl2·6H2O and ZnCl2 are introduced at the same time to achieve chemical activation and catalyze graphitization,which was time-saving and efficient,and the chemical properties were significantly improved compared to phenolic-based carbon spheres.In the experiment,the particle size of the RFC sample was adjusted by controlling the reaction conditions(alcohol-water ratio,resorcinol addition amount,catalyst concentration),and the particle size range was widely distributed,from 140nm(RFC2.8%-0.8-1:1)to 1600nnm(RFC2.8%-1.6-7).RFC2.8%-0.81:2 shows a relatively high BET specific surface area(419.91 m2/g),and the pore structure is dominated by micropores,Show that the material has a developed three-dimensional network structure.The electrochemical results show that:which has 139 F g-1 at a current density of 0.5A g-1,the current density increased from 0.5 A g-1 to 20 A g-1,showing a capacity retention rate of 74.09%.The capacity retention rate of the RFC1.4%-1.2-1:2 sample at a current density of 5A g1 for 10,000 cycles is 109.15%,and its Coulombic efficiency is close to 100%,showing excellent cycle stability.After KOH activation,the specific surface area increased to 1,235.62 m2/g,It further illustrates that the well-developed network structure of the carbon ball itself makes the activation work inside the material,and the specific capacitance was 203 F g-1 at a current density of 0.5 A g-1,and the current density increased from 0.5 A g-1 to 20 A g-1 shows a capacity retention rate of 78.4%;the capacity retention rate for 5000 cycles at a current density of 5A g-1 is 98.00%,showing excellent cycle stability.Ni-doped phenolic-based carbon spheres are heat-treated to achieve the purpose of catalyzing graphitization,thereby improving the conductivity of the material.In order to explore the optimal conditions for metal Ni to catalyze graphitization,graphitized carbon aerogel microspheres were prepared by controlling the amount of Ni addition and the heat treatment temperature.The results showed that GRFC1-900 reached 76.74%graphitization degree and had the lowest ID/IG value,indicates that it has a high degree of crystallinity of the graphite structure.The BET specific surface area decreased from 455.93 m2/g to 343.01 m2/g,This can be attributed to the closed cells formed by the"liquefaction migration" of Ni.Through the above exploration,the best preparation conditions of phenolic-based carbon spheres and the best conditions for Ni-catalyzed graphitization were obtained.On this basis,the introduction of melamine as a nitrogen source,a one-pot method was used to prepare nitrogen-doped porous graphitized carbon microspheres(NPGRFC).The experiment found that the amount of melamine added to the NPGRFC sample The particle size has a significant impact,ranging from 700nm(NPGRFCl-4)to 1400nm(NPGRFC34),and the surface of the sample is covered wth a layer of flake material and it is common,because the nitrogen-containing gas released during the pyrolysis of MF will continuously blow the pyrolyzed MF to form a sheet-like intermediate and cover the outer surface of the MRF.The addition of ZnCl2 reduces the content of oxygen-containing functional groups in the sample,and its chemical activation makes the specific surface area of the sample as high as 2130.60 m2/g,and the pore structure is mainly microporous;The welldeveloped network structure of the phenolic-based carbon ball itself provides more sites for activation and catalytic graphitization;XRD results show that the graphitization degree is as high as 94.19%;XPS results show that the amount of melamine added is proportional to the amount of nitrogen doped within a certain range;among them,the NPGRFC2-4 sample performance it has the best electrochemical performance.It shows a high specific capacitance of 218 F g-1 at a current density of 0.5 A g-1,and the current density increases from 0.5 A g-1 to 10 A g-1 It exhibits a capacity retention rate of 87.27%,a capacity retention rate of 108.80%for 10,000 cycles at a current density of 5 A g-1,and a coulombic efficiency of 100%,showing excellent cycle stability.The nitrogen-doped porous graphitized carbon spheres prepared by the one-pot method can achieve more ideal electrochemical performance than the current carbon ball materials,and the advantages of time-saving,safe,and lowcost experiments have become its potential advantages.