Study On Synthesis And Modification Of Manganese-based Cathode Materials For Aqueous Zinc-ion Battery

Aqueous zinc-ion batteries have become the next generation of new green batteries in recent years because of their low cost,high energy density,good safety and eco-friendly.Among the numerous cathode materials,the manganese-based material is considered as a promising cathode material for zinc ion batteries because of its rich resources,low toxicity,low cost and abundant valence.However,the poor conductivity of manganese-based materials and the volume changes during the circulation process lead to the capacity fading,which limits their further large-scale application.In order to solve the above problems of manganese based materials,in this thesis,metal organic framework materials are used as precursors to prepare Mn₂O₃ materials and modify Mn₂O₃/In₂O₃ materials by calcination;Further synthesis of Mn O@C hollow porous polyhedron is thermal reduction of carbon-coated Mn₂O₃ material.In addition,carbon cloth with good conductivity is used as the flexible substrate,and Mn O₂nanosheet material is successfully loaded on the surface of carbon cloth by hydrothermal method.The electrochemical properties of the above materials are evaluated as cathode material for aqueous zinc ion battery,respectively.1.Mn-MOF precursor was prepared by solvothermal method and Mn₂O₃material was obtained by further calcination.The influence of different heat treatment conditions on the morphology and electrochemical properties of the Mn₂O₃ material was explored.XRD results show that all the products at the calcination temperature of 750℃are Mn₂O₃.SEM results show that the material has a polyhedron morphology.Electrochemical tests show that the Mn₂O₃ material obtained by calcination at 750°C for 4 h has the most excellent electrochemical performance.In order to further enhance the electrochemical performance,Mn₂O₃/In₂O₃composites were made by calcining the Mn-MOF precursor mixed with an appropriate amount of In³⁺ions.The characterization results show that the addition of indium ion does not change the morphology of Mn₂O₃.Electrochemical tests show that a high reversible capacity of 267.4m Ah/g is obtained over 300 cycles at 300 m A/g,which is 63.3 m Ah/g higher than the pure Mn₂O₃ sample.After the appropriate amount of In³⁺ions are added,the ion diffusibility of the material is significantly improved which is deduced from the CV and EIS spectra.2.The Mn O@C porous hollow polyhedron was obtained by using the Mn₂O₃ polyhedron as the precursor and the polyvinylpyrrolidone as the carbon source coated on its surface and treated at high temperature under an inert atmosphere.The XRD results show that the Mn O diffraction peak does not appear in the diffraction peak of the carbon material,which preliminaries indicates that the carbon exists in an amorphous state.SEM results show that Mn O@C material has a porous hollow polyhedron and that the covered carbon layer can be clearly observed.Electrochemical tests show that the Mn O@C electrode material has a reversible capacity of 150 m Ah/g over 240 cycles at 300 m A/g,and the maximum specific capacity can reach 435.8 m Ah/g;and at a current of 1 A/g for 750 cycles,the specific capacity is stable at 135.1 m Ah/g,showing a good electrochemical performance.3.The manganese dioxide material loaded on carbon cloth was prepared by hydrothermal method.XRD test results show that the synthesized material is layeredδ-Mn O₂.SEM results show thatδ-Mn O₂ material has a nanosheets morphology.Electrochemical tests show that at a current density of 300 m A/g,Mn O₂@CC reveal a reversible capacity of 187.4 m Ah/g after 110cycles;at a current density of 1 A/g,the capacity stabilizes at 93.1 m Ah/g over 700 cycles of material.