Research On Structure Control And Potassium Storage Performance Of Doped Hollow Carbon Spheres

The huge demand for energy in human society has led to the depletion of fossil fuels.Therefore,it is urgent to develop new and stable energy storage technologies to store renewable energy sources,such as wind and solar energy,to meet the growing energy demand.Potassium ion batteries（PIBs）are considered to be promising potential candidates large-scale energy storage because of the abundance of potassium resources and similar physical and chemical properties to lithium.However,because the size of potassium ion（1.38?）is much larger than that of lithium ion（0.76?）,traditional alkaline metal battery anode materials exhibit slow potassium insertion kinetics,low potassium storage capacity,and poor rate and cycle performance.Therefore,it is of great significance to develop a new type of potassium ion anode material with excellent electrochemical performance.Aiming at developing a potassium ion battery anode material with excellent electrochemical performance and investigating the related problems of carbon anode materials,this paper designed heteroatom-doped hollow carbon spheres and studied the influence of heteroatom doping on its potassium storage performance.The research content includes the following two aspects:（1）Taking polystyrene spheres as a template and polypyrrole as the nitrogen source and carbon source,nitrogen-doped hollow carbon spheres（NHCs）with different wall thicknesses are obtained by one-step carbonization through changing the addition ratio of polypyrrole.The addition amount of pyrrole on the wall thickness of NHCs are explored as well as the the electrochemical performance of hollow carbon spheres in potassium storage.It is found that NHCs-20 has a three-dimensional hollow structure,suitable wall thickness and nitrogen atom doping characteristics,which is conducive to the insertion and extraction of potassium ions,and the introduction of more potassium active sites.The potassium storage capacity is as high as 327.8 m A h g^–1 at a current density of 100 m A g^–1,and maitains 95.6%of the initial stable capacity after 200 cycles.When the current density is increased to 1000 m A g^–1,NHCs-20 also exhibits a reversible specific capacity of 250.5 m A h g^–1,demonstrating its excellent cycle stability and rate performance.（2）In order to further improve the energy density and rate performance of the doped hollow carbon spheres,sulfur and nitrogen co-doped porous hollow carbon spheres are prepared by selecting carbon spheres with appropriate wall thickness and sulfur powder as sulfur source.The successful incorporation of sulfur atoms not only brings defects and more active sites for potassium storage,but also provides additional capacity contribution due to the reversible oxidation-reduction reaction with potassium,.In addition,the sulfur powder also plays a role in pore formation as a dopant.The obtained sulfur/nitrogen co-doped porous hollow carbon spheres（S/N-PHCs）shows a high specific surface area(502.2 m² g^–1)and large pore volume(0.196 cm³ g^?1).Therefore,the S/N-PHCs electrode can provide a high specific capacity of 460.6 m A h g^–1 at a current density of 100 m A g^–1,with an initial coulombic efficiency of 67.7%,and excellent rate capability of 228.1 m A h g^–1 at5000 m A g^–1.