Study On The Microstructure And Electrochemical Properties Of MOFs Derived Carbon Matrix Composites

Carbon materials have the characteristics of stable structure,strong chemical stability,good mechanical properties,large specific surface area and many reactive sites.They are widely used in energy storage,gas adsorption,catalysis and other fields.Carbon materials have shortcomings such as low theoretical specific capacity,poor cycle stability,low electrical conductivity and poor electrochemical performance,which restrict the application of carbon materials in the field of energy storage.New anode materials have become a hot research topic in the field of energy storage.The advantages of transition metal oxide materials such as large theoretical specific capacity and high safety have attracted the attention of researchers,but their structural instability,small specific surface area,few reactive sites and low electrical conductivity have restricted their development.In view of the above problems,this paper uses spinning carbon,three-dimensional graphene(3DGF),three-dimensional porous carbon(3DPC)as carbon substrate materials,combined with Zn-MOFs,Co-MOFs and Zn/Co-MOFs precursors,to prepare four carbon-based composite materials to study the influence of the microstructure of materials on the electrochemical performance.Porous CNFs(carbon nanofibers)materials are prepared by electrostatic spinning and thermal calcination,using Zn-MOFs polyhedral particles as precursors.Solvothermal and thermal calcination methods are used to prepare 3DGF/Co3O4 nanosheet composites.Using Co-MOFs as a precursor,it is compounded with three-dimensional porous carbon-based(3DPC),and solvothermal and thermal calcination are used to prepare 3DPC/Co/CoO composite materials.Using Zn/Co-MOFs as the precursor and nickel foam as the substrate,ZnO/Co3O4/C porous core-shell structure materials are prepared by solvothermal and thermal calcination methods.The SEM,Raman,BET,TEM,XRD,TGA and XPS are used to study Zn-MOFs polyhedron particles,Co-MOFs polyhedron particles,porous CNFs materials,3DGF/Co3O4 nanosheet composites and ZnO/Co3O4/C porous core-shell structures.The results show that the one-dimensional porous CNFs material has a diameter of 0.8?1?m,and the surface shows coarse pores and fine pores with a diameter of 100?300 nm;3DGF/Co3O4 nanosheets have a radial size of about 2?m and a longitudinal size of 20nm.Interlace to form a three-dimensional pore structure with a pore diameter of 0.2?2 ?m;3DPC/Co/CoO has a porous pore structure with a particle pore size of 30-50 nm,a specific surface area of 13 m2 g-1,and a carbon based pore size of 10-70 ?m;ZnO/Co3O4/C has a porous core-shell structure with a core-shell particle size of 700-800 nm,a pore size of 10-25 nm,and a specific surface area of 52 m2 g-1.The electrochemical workstation and battery test system are used to prepare the cyclic voltammetry,AC impedance,constant current cycle,charge and discharge characteristics and rate performance of the composite materials.The results show that the one dimensional porous CNFs at a current density of 100 mA g-1,after 200 cycles,the specific discharge capacity can reach 520 mAh g-1,the capacity decay rate is 10%,and the minimum diffusion coefficient of lithium ions is 10-11 cm2 s-1;the specific discharge capacity of 3DGF/Co3O4 nanosheet composites in the first cycle reaches 800 mAh g-1,and at a current density of 1000mA g-1,the specific discharge capacity remains 280mAh g-1;3DPC/Co/CoO composite maximum Coulomb efficiency of the material is 90%.At 100 cycles,the Rct is only 25?,the conductivity is 0-20 s/m,and the specific discharge capacity remains 300 mAh g-1 at a current density of 1000 mA g-1;Z1nO/Co3O4/C composite material has a discharge capacity of 1,250 mAh g-1 in the first lap and a maximum Coulomb efficiency of 100%.At 200 mA g-1 current density,the capacity decay rate is 10%.At 1000 mA g-1 current density,the discharge specific capacity remains 500 mAh g-1,and the minimum diffusion coefficient of lithium ions is 7×10-8 cm2 s-1;This paper uses metal semiconductor contact theory and molecular orbital theory to establish related models,and studies the contact interface of two types of electrode materials,carbon-based semiconductors,electrode electrolyte contact interface,and charge-discharge mechanism from an energy perspective.The results show that the precursor conversion porous CNFs material and the 3DGF/Co3O4 nanosheet composite electrode material have a single lithium ion intercalation mode,the electron barrier layer height of the carbon-based semiconductor contact interface changes little,and the electron transfer efficiency and Coulomb efficiency are low.During the recycling of the precursor continuum polyhedral particles and core-shell particles,the semiconductor side energy band of the electrode electrolyte interface has a small degree of bending,the quasi-level Ee position and the charge and discharge rate change are small,the electrode electrolyte interface is stable,and the cycle stability is high.The relationship between the microstructure and electrochemical performance of the precursor converted porous CNFs material and 3DGF/Co3O4 nanosheet composite electrode material is studied and a lithium insertion model is established.The results show that after electrode cycling,the porous structure of the porous CNFs electrode material remains,and the electrode material forms a porous embedded mode;the 3DGF/Co3O4 nanosheet electrode material forms a"top cross-linked structure",and the electrode material forms a channel embedded mode;the nanosheet composite electrode material has the electric double layer capacitor structure reduces the battery capacity decay rate.The relationship between the microstructure and electrochemical properties of the 3DPC/Co/CoO and ZnO/Co3O4/C composite electrode materials of the continuation of precursors is studied and a lithium insertion model is established.The results show that after electrode cycling,Co improves the conductivity of the composite electrode material,the carbon-based pore structure remains,the electrode material forms a porous plus channel embedding mode;the ZnO/Co3O4/C electrode material structure is completed,the pore structure appears on the particle surface,and the electrode material forms a porous hole-embedded embedding mode;core-shell structure avoids direct contact between electrode material and electrolyte,reduces electrolyte decomposition,alleviates internal stress changes,and reduces capacity attenuation rate;In summary,the use of precursor continuous single metal oxide and bimetal oxide carbon-based semiconductor contact interface and electrode electrolyte contact interface structure can improve the cycle stability of the electrode material and the ability to intercalate lithium.It is the modification of oxide materials and the development of new electrode materials which provide theoretical basis.