Application Of Nitrogen-doped Porous Carbon In Sodium Ion Batteries

Sodium ion battery?SIBs?has attracted more and more attention due to its advantages of low cost and abundant resources.However,due to the large size of sodium ions?Na⁺?,it is difficult for them to be embedded and released during charging and discharging.Therefore,it is necessary to study electrode materials with large interlayer spacing and active sites for the rapid transport and storage of sodium ions.This paper successfully designed and prepared a kind of 3D porous carbon that can be used in sodium ion batteries.The porous carbon not only has a larger structure of expanded graphite layer,but also has a rich vacancy of nitrogen atom doping,which improves the fast storage performance of sodium ions.Nitrogen-doped porous carbon?NPC?was successfully prepared by using asphalt as raw material,magnesium oxide?MgO?as template and urea as nitrogen source.The microstructure and electrochemical properties of the materials were characterized by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,XRD,XPS,Raman,FTIR,charge and discharge tester,and electrochemical workstation.The results showed that NPC had three-dimensional interlaced porous channels,larger graphite layer spacing,large specific surface area(322.6 m² g^-1)and high nitrogen content?6.05 wt.%?.This three-dimensional interlaced porous network structure shortens the diffusion distance of sodium ions,improves the transport and electron transfer of sodium ions,and provides a place for the rapid storage of sodium ions.At the same time,the high content of nitrogen doping makes NPC have more defects,and provides more active sites for the insertion/prolapse of sodium ions.Based on the above unique microstructure,NPC electrode has a high reversible capacity(198.9 m Ah g^-1)at the current density of 2.0 A g^-1 and cycling stability(capacity retention rate of 99%after 900 cycles at the current density of 5.0 A g^-1).In addition,the capacitance effect of NPC electrode and the sodium ion diffusion rate were calculated.The results showed that the capacitance effect of NPC electrode was 53%,80%and 84%respectively at the scanning rate of 0.1,0.4 and 1.0 m V s^-1.In addition,the sodium ion diffusion rate of NPC electrode during charging and discharging was 1.66×10^-9 cm²s^-1 and 3.78×10^-9cm²s^-1,respectively.By studying the effect of carbonization temperature on the structure of nitrogen-doped porous carbon,it was found that with the increase of carbonization temperature,the degree of graphitization of nitrogen-doped porous carbon gradually increased,and the spacing between graphite layers gradually decreased.Electrochemical results showed that the sodium storage capacity of NPC was higher than that of NPC8 and NPC9.It is shown that it is feasible to prepare porous carbon for sodium ion batteries by adding MgO and nitrogen atom doping.Based on the above special structure and excellent electrochemical properties,NPC is expected to become a new generation of sodium ion battery electrode material.