Preparation And Electrochemical Properties Of Manganese-based Composites Derived From Metal Organic Frames

Rechargeable aqueous zinc ion batteries(ZIBs)are a low-cost,safe and environmentally friendly rechargeable battery that benefits from zinc abundance,low REDOX potential,biocompatibility and high theoretical capacity(819 m A h g^-1).Due to the strong electrostatic contact between zinc ions,finding suitable cathode materials for ZIBs is a key challenge.Compared with other cathode materials,mangan-based compounds are very suitable as electrode materials for ZIBs due to their polyvalence state.However,their serious capacity attenuation and low conductivity affect their zinc storage performance.Metal-organic framework compounds(MOFs)not only have high specific surface area,but also have stable porous junctions.In this paper,the Mn-based two-component composites derived from MOFs were studied in order to improve the capacity decay of Mn-based compounds,structure instability and other problems,and improve the electrochemical performance.The main contents of this paper are:(1)The rod-like Mn O₂/ZIF-8 precursors were synthesized by hydrothermal method and then annealed to obtain Zn Mn₂O₄/Mn₂O₃composite.The morphology and structure of Zn Mn₂O₄/Mn₂O₃were studied by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The Zn Mn₂O₄/Mn₂O₃electrode has a high discharge specific capacity of 240 m A h g^-1(current density of 100 m A g^-1).The long cycle performance was tested at a current density of 1000 m A g^-1,and the discharge specific capacity was able to reach 80 m A h g^-1.In addition,the electrochemical kinetics and reversible storage mechanism of Zn²⁺were characterized by constant current batch titration(GITT),ex situ XRD,XPS and Raman spectroscopy analysis(Raman)characterization.(2)ZIF-8,Mn-MOF and ZIF-8/Mn-MOF materials were synthesized by solvothermal method.Compared with pure ZIF-8 and Mn-MOF,ZIF-8/Mn-MOF composites have high capacity and good cycling stability.At the current density of 100m A g^-1,the specific discharge capacities of ZIF-8,Mn-MOF and ZIF-8/Mn-MOF composites are 33.3 m A h g^-1,60.6 m A h g^-1 and 111 m A h g^-1 after 100 cycles.The excellent electrochemical performance is attributed to the synergistic effect of ZIF-8and Mn-MOF.(3)Mn S/(Mn,Zn S)@NS-C composites were prepared by curing and calcination of ZIF-8/Mn-MOF precursors.The EDX test of Mn S/(Mn,Zn S)@NS-C proves that S,C and N elements are evenly distributed in Mn S/Zn S@NS-C.At the current density of100 m A g^-1,Mn S/(Mn,Zn S)@NS-C(230 m A h g^-1)electrode has a higher discharge specific capacity than Zn S@NS-C(45 m A h g^-1)and Mn S@S-C(101 m A h g^-1)electrode.The storage mechanism of Zn²⁺was preliminarily explored by ex situ XRD characterization.(4)Mesoporous carbon materials(MCMS)with different activation ratios were prepared from Ginkgo biloba flesh.According to SEM and electrochemical performance tests,the optimal activation ratio of MCMS was 1:2(MCM2)between Ginkgo meat and KOH.We have successfully synthesized Zn Mn₂O₄/MCM2composite material,which not only provides an efficient electron transport pathway,but also stabilizes the composite structure to reduce volume expansion during cycling.The maximum specific discharge capacity of 296.1 m A h g^-1 and stable cycle life of Zn Mn₂O₄/MCM2 electrode at a current density of 100 m A g^-1 were obtained due to the synergistic effect.The mechanism was analyzed by ex situ XRD,and the emplacement/detachment of Zn²⁺in Zn Mn₂O₄/MCM2 electrode was investigated.