Structure Construction And Performance Of Manganese-Based Cathode Materials For Aqueous Zinc-Ion Battery

Aqueous zinc ion battery（AZIBs）is a new type of green secondary battery,which has attracted wide attention in recent years..Compared with traditional lithium-ion battery,AZIBs have the advantages of high safety,low cost and non-toxic environmental friendly,so it has a bright future in the field of large-scale energy storage.Among the cathode materials of AZIBs,manganese-based materials have attracted the most attention because of their low cost,low toxicity,high working voltage and multivalent state.However,the capacity decay caused by the structural collapse during cycling and the low conductivity hinder the development of the manganese-based cathode.In this thesis,the microstructures and morphologies of manganese-based compounds were controlled by conductive polymer and metal organic frameworks（MOFs）.The electrochemical properties of manganese-based cathode were improved by constructing spherical manganese-based compounds with heterogeneous core-shell and hollow structure.The specific research contents are as follows:MnCO₃@PPY cathode materials were synthesized by one-step hydrothermal method and in-situ chemical oxidative polymerization.The results show that the PPy layer with a thickness of about 100 nm is successfully grown on the surfaceof MnCO₃microsphere.The coating of PPy layer can alleviate the structural collapse during the cycling process,and greatly improve the conductivity of the cathode.AZIBs assembled with MnCO₃@PPY cathode showes great cycling stability and satisfactory rate performance.which maintain the capacity of 252 m Ah g^-1after cycling for 110times at 200 mAg^-1and reach the capacity of 203.5 m Ah g^-1even after cycling for1200 times at 1000 mAg^-1.In addition,the phase changes during the charge-discharge process were analyzed by ex-situ XRD.The results show that MnCO₃@PPy is a kind of conversion cathode material and MnCO3 is converted to MnO_xduring the first charge process.In the subsequent charge-discharge process,MnO_xplays the most important role in energy storage.And its energy storage mechanism is mainly attributed to the coordinated extraction/intercalation of H⁺and Zn²⁺ions.MnS@（Zn,Mn）S/C cathode materials were synthesized by a solution synthesis method and two-step vulcanization method.The results show that the construction of composite materials can improve the cycling performance of the cathode,and the MOF-derived carbon on the surface can also improve the conductivity of the cathode.After cycling at the current density of 200 mAg^-1for 100 times,the reversible specific capacity is 226.5 m Ah g^-1and the coulombic efficiency is 99.23%.After 1000 cycles at 1000 mAg^-1,the reversible specific capacity can still maintaine at 85.6 m Ah g^-1and the coulombic efficiency is 99.85%.The energy storage mechanism and electrichemical kinetics were also studied by ex-situ XRD.It was found that MnS@（Zn,Mn）S/C cathode gradually transform to MnO_xduring cycling.In the subsequent charge-discharge process,MnO_xplays the most important role in energy storage.And its energy storage mechanism is mainly attributed to the coordinated extraction/intercalation of H⁺and Zn²⁺ions.Mn₂O₃@ZnMn₂O₄/C hollow core-shell microspheres were synthesized by a solution synthesis method and one step oxidation method.The hollow structure and MOF-derived ZnMn₂O₄/C layer can reduce the structure collapse and dissolution caused by the volume change during cycling.The MOF-derived carbon layer on the surface of Mn₂O₃improves the conductivity of the cathode.In addition,the synergistic effect between ZnMn₂O₄and Mn₂O₃can also improves the properties of the cathode and enhances the structural stability of the cathode materials.Due to its unique structure and the synergistic effect between ZnMn₂O₄and Mn₂O₃,its high reversible capacity is undeniable,which reaches its maximum of 289.9 m Ah g^-1at 200mAg^-1and maintains the capacity of 203.5 m Ah g^-1after cycling for 700 times at1000 mAg^-1.In addition,the ex-situ XRD was used to characterize the Mn₂O₃@ZnMn₂O₄/C cathode under different charge-discharge states.The results show that the composition of Mn₂O₃@ZnMn₂O₄/C cathode is highly reversible,the energy storage mechanism of Mn₂O₃@ZnMn₂O₄/C cathode in the process of charge and discharge is mainly attributed to coordinated extraction/intercalation of H⁺and Zn²⁺.This thesis contains 41figures,2 tables and 172 references.