Morphological Control And Electrochemical Performance Of Nitrogen-doped Carbon Materials

Carbon materials have been widely used in the field of electrochemistry due to their excellent properties such as controllable specific surface area,high conductivity,low price,good chemical stability and thermal stability.With the development of technology,commercial carbon materials do not meet the needs of modern society.Recently,researchers have tried many methods to solve those problems,among which nitrogen doping in carbon materials or structural regulation at the nanoscale.Hence,we carried out a template method by using nitrogen containing polymer as carbon precursor,carbonation of high nitrogen doped hollow ball structure and honeycomb structure of carbon materials,discussed the impact of carbon material microstructure on its electrochemical properties.?1?Nitrogen-doped hollow carbon spheres,with controllable size and morphology,were successfully prepared with polystyrene as template and polypyrrole as carbon precursor by simple template carbonization method.By controlling the dosage of stabilizer,initiator and polymerization temperature,the polystyrene templates with good dispersion and sizes ranging from 60 nm to 150 nm were prepared.The effects of monomer content,template size,carbonization temperature and CO₂ activation time on the morphology and pore structure of nitrogen-doped hollow carbon spheres were discussed in detail.With the increase of the amount of pyrrole monomer,the wall thickness of the hollow carbon ball also increased?15?24nm?,and the carbon ball gradually adhered to each other,and the dispersion became worse.By controlling the size of the template particle size,the particle size of the hollow carbon sphere can be adjusted.However,as the template particle size decreased,the dispersion of the hollow carbon sphere became worse.With the increase of carbonization temperature,the thickness of hollow carbon ball wall became thinner and the shell crushing rate increased,the disorder gradually reduceed,and the specific surface area increased.Within a certain activation time,the hollow carbon sphere can basically maintain the spherical shape,and the specific surface area increased from 86.5 m²/g to 406.9 m²/g.?2?When nitrogen doped hollow carbon spheres are used as anode materials for lithium ion batteries,due to their rich nitrogen content?8.89 at%?.The effects of carbonation temperature,particle size,wall thickness,surface morphology and CO₂activation on the electrochemical properties of hollow carbon spheres were systematically investigated..Under the condition of carbonization temperature,the degree of graphitization and nitrogen content changed,which influenced in the hollow carbon electrochemical performance.When the temperature was 800?.Under the current density of 5 A/g after 3500 cycle,the reversible capacity was still as high as231 mAh/g.When the NHCs thickness increased from 15 nm to 24 nm,the NHCs-555,with the largest wall thickness,had a reversible capacity is 585.7 mAh/g after 300cycles under the current density of 0.5 A/g.It may because the NHCs-555 spherical shell with larger thickness has higher strength,smaller spacing between graphite layers and fewer defects,which made it less likely to deform during the cycle and formed a more stable SEI film,thus showing excellent electrochemical properties.When the particle size decreased from 160 nm to 50 nm,the serious agglomeration and poor dispersibility of the particles had an adverse impact on the electrical properties of lithium ion battery,showing that NHCs with the smaller particle size,the porr its ratio performance and cycle stability performance.CO₂ activation effectively improved the ion transfer rate at high current density,it can conducive to the materials cycle stability.?3?Honeycomb nitrogen-doped porous carbon materials with rich pore structure and 15.31 at.%were prepared using SiO₂ as template and polydiaminopyridine as carbon precursor.The pure diaminopyridine carbonized material?NC?and honeycomb carbon material?HNC?were compared and analyzed on the structure and electrochemical properties.The results show that HNC had better performance than NC without hole forming.At the current density of 0.1 A/g,the specific capacity value of HNC was 398 F/g and the capacity retention rate reached 110.4%after 5000cycles at the current density of 2 A/g.When carbonized at different temperatures form700?to 800?,HNC-800 had the optimal performance.when the current density of 0.1 A/g,the specific capacity of HNC-800 reached to 385 F/g.