Construction Of Defective Carbon Materials Based On Nitrogen Doping And Its Electrochemical Mechanism

Due to the low theoretical capacity(372 m Ah g^-1),graphite can not meet the energy demand of large electronic equipment such as electric vehicles.Therefore,it is urgent to find new cathode materials for the energy development of modern society.Defective carbon has been widely studied because it can provide more lithium ion insertion sites and higher electronic conductivity.Based on the above theory,this paper selects the defective carbon material as the research object,starts with the defect type and mechanism,and uses a simple preparation method to improve the capacity of carbon material and improve the problem of poor high rate performance.The main work contents are as follows:（1）Nitrogen self doped defective carbon micro blocks were prepared by high temperature solid state method.X-ray photoelectron spectroscopy（XPS）analysis shows that the nitrogen content is increasing,and all contain three defect types of nitrogen:pyridine nitrogen,pyrrole nitrogen and graphitization nitrogen.Transmission electron microscopy（TEM）and scanning electron microscopy（SEM）showed that all samples were carbon micron blocks,and there were local turbine like lattice fingerprints in the samples.Self nitrogen doped micron carbon blocks have excellent cycle performance and ultra-high rate capacity.When the current density is 1 A g^-1 and 2 A g^-1,the average magnification capacity can be maintained at 319.0 m Ah g^-1 and 193.5m Ah g^-1,respectively.When cycling at 5 A g^-1,the discharge capacity can still be maintained at 58.3 m Ah g^-1 after 3500 cycles.The defects caused by nitrogen doping not only improve the reaction activity and electronic conductivity,but also enhance the diffusion kinetics of lithium ion.（2）Using polyacrylonitrile as carbon source and nitrogen source,controllable defect type carbon was synthesized by hydrothermal method and microwave synergistic hydrothermal method.This method greatly shortens the preparation time and improves the electrochemical properties of amorphous carbon.XPS analysis showed that the content of pyridine nitrogen increased and the graphitized nitrogen disappeared in the amorphous carbon block.The results show that the nitrogen doping position of amorphous carbon block can be adjusted by hydrothermal method.The microstructure observation shows that the nitrogen self doped carbon is nano carbon sphere and micron carbon block.Self nitrogen doped micron carbon blocks have excellent cycle performance and ultra-high rate capacity.When cycling at 0.5 A g^-1,the discharge capacity remains 356.6 m Ah g^-1 after 1000 cycles.Even after cycling at 5 A g^-1,the rate capacity remained at 183.3 m Ah g^-1 after 300 cycles.This defect is caused by pyridine nitrogen self doping,which not only improves the structural stability of the material,improves the reaction activity and electronic conductivity,but also enhances the diffusion kinetics of lithium ion.（3）The principle that the electron cloud density of nitrogen atom is reduced by the coordination reaction between nickel ion and nitrogen atom.Using polyacrylonitrile and melamine as carbon and nitrogen sources,defective carbon with adjustable nitrogen doping sites was synthesized by microwave solid-state method under the control of nickel acetate.XPS analysis showed that the nitrogen content in the sample was as high as 11.81%,the pyridine nitrogen content increased significantly,and the graphitized nitrogen disappeared.SEM showed that nitrogen self doped carbon was micron carbon block.Self nitrogen doped micron carbon blocks have excellent cycle performance and ultra-high rate capacity.When the current density is 1 A g^-1 and 2 A g^-1,the average magnification capacity can be maintained at 374.4 m Ah g^-1 and 147.2 m Ah g^-1,respectively.When cycling at 1 A g^-1,the discharge capacity can still be maintained at373.4 m Ah g^-1 after 200 cycles.The defects produced by pyridine nitrogen are conducive to the intercalation of lithium ions and increase the electronic conductivity.