Theoretical Calculation And Potassium Storage Performance Of Nitrogen And Sulfur Doped Porous Carbon And Sb/C Composites

Potassium reserves are abundant,redox potential is low(K/K+,-2.93V),and K+has a relatively low Lewis acidity in the electrolyte.These advantages make the potassium ion batteries stand out in terms of cost,life,power and energy density.Outstanding advantages make it an ideal choice for large-scale energy storage.However,the K+radius and mass are large,and the diffusion rates are slow in the electrode material,which poses a great challenge to the development of electrode material for the potassium storage.Carbon materials are cheap and environmentally friendly,and can form KC8 compounds with potassium;metal antimony can undergo multi-electron alloying reaction with potassium to form K3Sb to obtain higher capacity.Therefore,carbon-based and antimony-based materials are ideal for storing potassium anode materials.However,the potassium-ion storage capacity of the carbon material is low,the rate performance and the cycle stability are poor,and the volume change of the metal Sb during the alloying process is large,and the cycle capacity is seriously attenuated.In view of the above problems,the main research contents of this paper are as follows:(1)The properties of the electronic structure and potassium adsorption behavior of nitrogen-doped graphene materials were studied by first-principles calculation.The results show that in the nitrogen-doped graphene material,pyridine nitrogen and pyrrole nitrogen can significantly enhance the conductivity of the material and the adsorption energy of the pyridine nitrogen to the K atom is-2.78 eV.The adsorption energy of pyrrole nitrogen to K atom is-2.70 eV,which further promotes the adsorption of K+on the electrode surface and enhances the electrochemical performance.The in-situ pyrolysis method was used to prepare the porous carbon materials with different nitrogen doping levels by controlling the proportion of nitrogen sources,and the potassium-ion storage performance was explored in detail.The porous carbon material with a nitrogen doping content of 12.44 wt%exhibited the most excellent rate characteristics(216 mAh g-1 at 2 A g-1)and cycle stability(229 mAh g-1 at a current density of 0.5 A g-1 after 800 cycles).(2)The properties of structure,electronic structure and adsorption behavior of sulfurdoped graphene materials were calculated by first-principles.The results show that sulfur doping enhanced the conductivity of the material,and the adsorption energy of the thiophene sulfur to the K atom is-4.13 eV,which greatly promotes the adsorption of K+on the electrode surface.On this basis,the porous carbon with different carbonization temperatures were designed and synthesized,and its sulfur doping modification was carried out to explore the effects of sulfur doping and carbonization temperature on the electrochemical properties of carbon materials.The results show that the sulfur doping can significantly improve the electrochemical performance of the porous carbon material.The electrochemical performance of SPC-600 is the best.Initial charge capacity is 417 mAh g-1 at a current density of 0.1 A g-1 and the reversible specific capacity still maintain 342 mAh g-1 after 100 cycles,indicating the good reversibility(82%).(3)The KxSb(x=0.5,1,1.25,3)alloy phases were studied using first-principles based on density functional theory.The results show that the volume expansion of Sb is 455%when K3Sb is formed by alloying with K.Therefore,different proportions of Sb/C composites were synthesized by ball milling in this paper.The results showed that when the composition ratio was Sb:C=3:7,the capacity after cycling was the highest and the cycle stability was the best.The reversible capacity reached 235 mAh g-1 after 100 cycles at 0.1 A g-1.