Electrode Design And Potassium Storage Mechanism Of Three-Dimensional Graphene-Based Composites

Potassium ion battery（PIBs）has abundant potassium storage resources,wide working potential window,good carbon anode electrode adaptation and so on,which has the potential to be a supplement to lithium-ion battery（LIBs）.However,the large ionic radius of K⁺poses a serious challenge to realizing the stable and efficient potassium storage for electrode materials.Among all kinds of carbon material anode,graphene has good mechanical strength,good electrical conductivity and rich active area,which can alleviate the problems of volume expansion and slow kinetics caused during K⁺insertion/extraction process,so it is a suitable anode electrode material for PIBs.However,the actual electrochemical performance of conventional two-dimensional flake graphene is not outstanding due to stacking reconstruction and interlayer conductive network fracture.Three-dimensional graphene materials modified with Fe compounds were prepared by a simple chemical blowing process.In this paper,three-dimensional graphene-based materials were prepared by chemical blowing method,its continuous conductive network was used to optimize the fine structure,active site and interface transmission.And the overall electrochemical performance of three-dimensional graphene-based materials was improved.The mechanism of potassium storage was studied systematically.The main research contents are as follows:（1）The composition of foaming agent was modified by adding trace amount of cobalt nitrate（Co（NO₃）₃·6H₂O）to ferric nitrate（Fe（NO₃）₃·9H₂O）,and polyvinylpyrrolidone（PVP）was used as carbon source.The three-dimensional graphene framework（Co-Fe₃C/3DG）with fewer layers and higher degree of graphitization was obtained by cobalt modification.Thanks to the continuous three-dimensional conductive network of the three-dimensional graphene framework,and the improvement of the degree of graphitization after cobalt modification.In specific potassium storage electrochemical performance test,Co-Fe₃C/3DG can maintain a reversible capacity of 196.1 mAh g^-1 after 100 cycles at 0.1 A g^-1 current density.（2）FeTe₂/3DG composites were constructed by using the confined structure of Fe₃C/3DG and the continuous three-dimensional conductive network.Using high temperature telluride solid phase,the electrochemically inert Fe₃C is transformed into an electrochemically active FeTe₂ phase.FeTe₂ will completely replace Fe₃C without changing the structure of graphene.The unique confined structure enables FeTe₂ to establish a stable interface contact with graphene,which ensures good dispersion of nano-Fete₂ and greatly reduces volume expansion during charging and discharging.Our designed FeTe₂/3DG has a reversible capacity of 540.8 mAh g^-1 after 30 cycles at 0.1 A g^-1.The reversible capacity of 1 A g^-1remains at 306.5 mAh g^-1 after 300 cycles.（3）Using Fe₃C/3DG as precursor,bidirectional phosphorus doped ferric selenide/three-dimensional graphene composites（DP-Fe₃Se₄/3DG）were prepared by simultaneous phosphorus selenization.Phosphorus doping into graphene increases the number of defect sites in graphene.At the same time,phosphorus doping iron selenide will increase the intrinsic conductivity of iron selenide and promote the active participation of electrons in the electrochemical reaction.Through first-principles calculation,clearing bidirectional phosphorus mixing strategy will increase the adsorption energy of K⁺and decrease the diffusion energy barrier between both interfaces.Bidirectional phosphorus doping engineering stimulates the potassium storage function of dual active centers,and the system’s"three-in-one"optimization strategy of confined,defect and interface engineering enables DP-Fe₃Se₄/3DG to achieve a balance in terms of capacity,rate and dynamics.The electrochemical potassium storage function of 3D graphene framework was developed to the maximum extent.Finally,the multi-step potassium storage mechanism of DP-Fe₃Se₄/3DG was analyzed by in-situ XRD and Operando Raman techniques.