Structural Optimization Of Carbonaceous Materials For High-Performance Potassium-Ion Batteries

Energy crisis and environmental pollution are major challenges facing the world today.How to realize the efficient conversion,storage and release of energy is a hot topic that academia and industry need to face together.Potassium-ion batteries（PIBs）have similar chemical properties and working principle as lithium-ion batteries.Meanwhile,PIBs hold the advantages of abundant resource reserves,high working voltage and low cost,which is the future star in the field of large-scale energy storage.However,the large ionic radius of K⁺leads to the low specific capacity,poor cycling stability and sluggish diffusion kinetics behavior in carbonaceous materials,which seriously hinders the practical application of PIBs.Therefore,the development of carbonaceous anodes with excellent potassium storage performance can accelerate the development of PIBs.In this thesis,aiming at the issues of short cycle life,poor rate performance and low specific capacity of carbonaceous anodes for PIBs,the potassium storage capability is improved by the strategies of heteroatom doping,regulating pore structure,introducing nano-metal particles and designing nano-structure.Thereby,the efficient preparation of carbonaceous materials with high specific capacity,high rate ability and long cycle life can be realized.The specific research contents and conclusions are summarized as follows:（1）Nitrogen/sulfur co-doped porous carbon（NSC）have large interlayer spacing and specific surface area,as well as abundant active adsorption sites,which help to enhance the adsorption capability of carbon materials for K⁺ions and reduce the diffusion energy barrier of K⁺ions in carbon materials.Therefore,the potassium storage performance of NSC material can be improved.The results of reaction kinetics and density functional theory（DFT）calculations indicate that NSC material exhibits enhanced capacitive adsorption property,fast charge transfer and K⁺diffusion kinetics behavior.As anode material for PIBs,NSC possesses reversible capacity of 302.8 m Ah g^-1 at 100 m A g^-1,and stable capacity of105.2 m Ah g^-1 at 2000 m A g^-1after 600 cycles,showing high potassium storage capacity and long cycle stability.（2）Oxygen-doped porous carbon materials（Ca-PC,Na-PC and K-PC）with different specific surface area and pore structure are prepared with metal organic acid salts as the precursors.Their potassium storage performances are further investigated.As a result,Ca-PC material has abundant porous structure,larger interlayer spacing and specific surface area,as well as higher oxygen-doping content.The enlarged interlayer spacing can reduce the diffusion energy barrier of K⁺ions,and the porous structure can alleviate the volume effect and provide transport channels for K⁺ions.Meanwhile,oxygen doping can induce structural defects and active sites,promoting the capacitive adsorption ability of Ca-PC.Benefiting from these effects,the potassium storage capacity of Ca-PC anode at 100,200,500,1000,2000 and 4000 m A g^-1 are 305.2,295.1,242.2,207.2,176 and 144.2 m Ah g^-1,respectively,indicating excellent rate performance.Even at high current density of 5000 m A g^-1,its corresponding potassium storage capacity after 2000 cycles can still maintain at 121.4 m Ah g^-1,suggesting superior cycling performance.（3）Co-NC composite composed of cobalt nanoparticles and nitrogen-doped graphitic carbon is prepared with Prussian blue analogs as the precursor.In the composite,cobalt nanoparticles are surrounded by the layers of nitrogen-doped graphitic carbon,and a core-shell structure is in-situ constructed,which endows Co-NC with fast and durable potassium storage behavior.Electrochemical data and DFT calculation results show that the three-dimensional conductive potassium storage network constructed by cobalt nanoparticles and nitrogen-doped carbon can promote charge transfer,increase K⁺adsorption sites and reduce K⁺diffusion energy barrier.Therefore,Co-NC anode can achieve high specific capacity of 305 and 208.6 m Ah g^-1 after 100 and 300 cycles at 50 and 100m A g^-1,respectively.Meanwhile,it exhibits reversible specific capacity of115.7 m Ah g^-1 after 1000 cycles at 500 m A g^-1,indicating excellent structural stability.（4）Zn-NPC composite containing trace metalic zinc and nitrogen/phosphorus co-doped carbon is prepared with zinc-based metal-organic gel as the precursor.Electrochemical data and DFT calculation results indicate that the introduction of trace metal zinc can improve the conductivity as well as electrochemical reactivity,promoting charge transfer and K⁺diffusion behavior.Meanwhile,nitrogen/phosphorus co-doping can enlarge the interlayer spacing and increase the active adsorption sites,endowing Zn-NPC with enhanced capacitive adsorption behavior.Therefore,the potassium storage capacity of Zn-NPC anode at 50 m A g^-1is 300.1 m Ah g^-1,and the corresponding initial Coulomb efficiency is as high as 57.67%.Additionally,the reversible capacity can still keep at 197.2m Ah g^-1 at 200 m A g^-1 after 1500 cycles,suggesting excellent cycling stability.（5）The phenolic resin precursor with concave surface is synthesized by organic molecular self-assembly polymerization reaction,followed by the preparation of concave carbon hollow spheres（CCHS）through a high-temperature carbonization process.The feasibility and potential advantages of CCHS as anode materials for PIBs are further studied and verified.As a result,CCHS has large specific surface area and interlayer spacing,and a low degree of graphitization.The finite element simulation results of von Mises stress demonstrate that the stress accumulation in porous concave hollow carbon spheres during the potassiation process is anisotropic,which is conducive to the formation of uniform stress distribution,thereby relieving the stress concentration effect and avoiding the structural deformation or structural failure during cycling.Benefiting from its structural advantages,the potassium storage capacity of CCHS anode still maintains at 104.9 m Ah g^-1 after 1340 cycles at a high current density of 4 A g^-1,corresponding to an extremely low capacity decay rate of 2.7%.There are 80 pictures,4 tables and 232 references.