Preparation And Potassium Storage Properties Of Diatomic-doped Coal Tar Pitch-based Carbon Materials

As"carbon peak"and"carbon neutral"formulation of objectives,the development of renewable and efficient energy storage equipment is becoming increasingly critical and urgent.Because of its abundant potassium resources,low cost and low voltage platform,potassium ion battery has gradually highlighted its great application potential in the field of large-scale energy storage.However,due to the large radius of potassium ions,it is easy to cause material volume expansion and pulverization during charge and discharge,which leads to poor cycle stability and rate performance.Well-designed anode materials are crucial for boosting the rate performance of potassium ion battery to alleviate the volume expansion caused by the charge and discharge process and to improve the low capacity.Coal tar pitch-based carbon materials have been widely used in the field of energy storage because of their wide range of sources,low price and good electrical conductivity.However,coal tar pitch-based carbon materials have the disadvantages of less carbon layer spacing and less potassium storage active sites.In this paper,the anode electrode material of potassium ion battery with high rate performance is designed by means of chemical property control,pore structure design and two-dimensional structure construction with coal tar pitch as carbon source.The specific research contents are as follows:（1）Nitrogen and fluoride dual-doped carbons were successfully prepared from coal tar pitch and NH₄F as nitrogen and fluorine sources.Due to the self-decreasing template of NH₄F,the material forms a unique honeycomb porous structure,which is beneficial to the full contact with electrode material and electrolyte and shortens the diffusion path of ions.The introduction of nitrogen and fluorine heteroatoms expands the carbon interlayer spacing and increases the active sites,thus improving the electrochemical properties of the materials.As the working electrode material for potassium ion half-cell,the capacity retention rate of the prepared sample is 80.5%after 400 cycles at a current density of 1 A g^-1.Even at 5 A g^-1current density,the specific capacity can be as high as 81.6 m Ah g^-1.（2）Using coal tar pitch as carbon source,Ammonium polyphosphate is a source of nitrogen and phosphorus,Na Cl as a template,nitrogen and phosphorus co-doped porous carbon materials were prepared by one-step carbonization.Meanwhile,the doping mechanism of nitrogen and phosphorus atoms in carbonization process is further analyzed by in situ Fourier transform infrared and synchronous thermal analysis.When the ratio of ammonium polyphosphate to coal pitch is 2:1 and the carbonization temperature is 700 ^oC,the phosphorus content of the prepared material can be as high as 3.15%,which is helpful to synchronize with 3.68%nitrogen to play the synergistic effect among heteroatoms.the prepared material as the working electrode material of potassium ion half cell,after 400cycles at 1 A g^-1 current density,the capacity retention is 81.8%.Even at a current density of10 A g^-1,it still showing a specific capacity of 126 m Ah g^-1.The excellent potassium storage performance is mainly attributed to the synergistic effect of nitrogen and phosphorus co-doping and its unique multistage pore structure.