Preparation Of Transition Metal Sulfide/Phosphate Composites And Their Electrochemical Sodium/Potassium Properties

With the rapid development of electronic equipment,electric vehicles and large-scale energy storage systems,the demand for energy storage materials is increasing.The wide application of lithium-ion batteries in these fields is severely constrained by the uneven distribution of lithium resources.Considering the similar positions of Li,Na and K in the periodic table and the natural resources rich in Na and K,sodium and potassium ion batteries have recently attracted more and more attention.So far,compared with lithium-ion batteries,sodium ion battery electrode material is very rare,only a few Na storage anode materials show a certain redox capacity and sufficient cycle capacity.The research on potassium ion batteries is still in its infancy,and the research on anode materials is mainly concentrated on carbon-based materials,but carbon-based materials only exhibit limited reversible capacity.Transition metal sulfur/phosphates,which have a wide range of sources and rich active sites,can be used as diverse electrode materials,which have attracted much attention in recent years.This project uses a thermal decomposition method to synthesize a composite material?SnS₂/NGS?of tin disulfide nanosheets and nitrogen-doped graphene.Preparation of a tin phosphide/redox graphene composite material?Sn₄P₃/RGO?uniformly distributed on reduced graphene oxide by mechanical ball milling,And their electrochemical storage of sodium/potassium properties.The specific research contents are as follows:1.Using SnCl₄·5H₂O as the tin source and CH₄N₂S as the sulfur source and nitrogen source,the composite material?SnS₂/NGS?on which the tin disulfide nanosheets were grown on nitrogen-doped graphene was prepared by thermal decomposition.When the prepared SnS₂/NGS composites are used as anode materials for sodium ion batteries,the specific capacity of reversible discharge is 333.7 mAh g^-11 after 200 cycles of current density of 500 mA g^-1.Even at a high current of 1800mA g^-1,the discharge specific capacity of 348 mAh g^-11 is still much larger than that of SnS₂.The materials were assembled into potassium ion batteries,The average discharge specific capacity at a current density of 400 mA g^-11 is 213 mAh g^-1,the capacity of SnS₂/NGS composites is much larger than that of pure SnS₂ electrodes at different current densities.The excellent electrochemical performance of SnS₂/NGS comes from the synergistic action of tin disulfide and nitrogen-doped graphene,which can effectively inhibit the adverse reaction between soluble sodium polysulfide or potassium and electrolyte,and make the SnS₂/NGS electrode have excellent structure and cyclic stability.2.Tin phosphide/reduced graphene composite?Sn₄P₃/RGO?with uniform distribution on the reduced graphene matrix was synthesized by mechanical ball milling using Sn powder,red phosphorus and reduced graphene oxide as the main reactants.The results show that the size of Sn₄P₃ nanoparticles grown in the RGO matrix is more uniform and the size is about 5-10 nm.When used as anode electrode for sodium ion batteries,Sn₄P₃/RGO can still maintain a reversible capacity of 291mAh g^-11 at a current density of 600 mA g^-11 for 150 cycles.In the test of the magnification ratio,Sn₄P₃/RGO also showed better rate performance.As anode electrode of a potassium ion battery,it is found that the prepared Sn₄P₃/RGO has a higher initial reversible capacity(452.6 mAh g^-1)and a better rate capacity(116.4mAh g^-1)even at a high current density(800 mA g^-1)and maintains a capacity of157.3 mAh g^-11 after 60 charge-discharge cycles at a high current density of 600 mA g^-1.The experimental results show that the growth of Sn₄P₃ on the RGO layer can buffer the change of the volume of Sn₄P₃ in the process of charge and discharge,so that the material exhibits good electrochemical performance.