Preparation And Electrochemical Properties Of MOF-based Derived Transition Metal Sulfides

Metal-organic frameworks(MOFs)are a kind of porous materials composed of metal ions and organic ligands self-assembled by coordination bonds.Compared with traditional porous materials,different functional groups and metal centers can be introduced through reasonable design,and can also be used as self-sacrificing templates to prepare MOFs derived materials.MOFs have the characteristics of large specific surface area,high porosity and rich REDOX activity,etc.,showing a broad application prospect in catalysis,energy storage and other fields.However,the poor conductivity of most MOFs and the serious volume expansion during charge and discharge limit their applications in the field of electrochemical energy storage.In order to solve the above problems,the introduction of new functional components in MOFs can improve their poor electrical conductivity and stability.In recent years,MOFs derived materials inherit the advantages of MOFs and have some unique properties,which have attracted extensive attention of researchers.In this thesis,MOFs composites and MOFs-derived transition metal sulfide/carbon composites were prepared by a simple method,and used as anode materials for lithium ion batteries.The specific content is as follows:(1)Co-TCPP MOF nanosheets were synthesized by a simple one-step hydrothermal method using meso-tetrakis(4-carboxyphenyl)porphyrin(TCPP)as ligand and metal cobalt ion through coordination bond self-assembly to synthesize Co-TCPP MOF nanosheets.In addition,reduced graphene oxide(r GO)was added to Co-TCPP MOF to synthesize Co-TCPP MOF/r GO flower-like ultra-thin composites.The addition of r GO not only eases the stacking of layered Co-TCPP MOF,but also improves the conductivity of MOF.Combining the advantages of Co-TCPP MOF and r GO,flower-like Co-TCPP MOF/(15 wt%)r GO composite has excellent lithium storage performance as a negative electrode material for lithium-ion batteries.After 100 cycles at a current density of 100 m A g-1,the reversible specific capacity Keep it at1050 m Ah g-1.Even at a high current density of 1000 m A g-1,it can still maintain a reversible specific capacity of 650 m Ah g-1 after 300 cycles.(2)Cu-TCPP MOF nanosheets were synthesized by a simple hydrothermal method using meso-tetrakis(4-carboxyphenyl)porphyrin(TCPP)as ligand and metal copper ions through coordination bond self-assembly.Then,using thioacetamide(TAA)as the sulfur source,Cu S/Cu-TCPP MOF-x composites were synthesized by in-situ growth of copper sulfide nanoparticles on the surface of Cu-TCPP MOF nanosheets by hydrothermal method.By controlling different reaction conditions,Cu S nanoparticles with different densities were grown on Cu-TCPP MOF nanosheets.Compared with pure Cu-TCPP MOF nanosheets,the copper sulfide nanoparticles in the Cu S/Cu-TCPP MOF-12 composite material improves the conductivity and stability of the nanosheets,and its lithium storage performance is improved.After 100 cycles at a current density of 100 m A g-1,the reversible specific capacity of the Cu S/Cu-TCPP MOF-12 composite remained at 400 m Ah g-1.(3)Nickel chloride hexahydrate and 5-Mercapto-1-phenyl-1H-tetrazole are hydrothermally reacted to form Ni-PTA MOF microspheres,which are then used as a precursor to pyrolyze and vulcanize at high temperature to obtain a hollow Microsphere Ni Sx@NSC composites.During the pyrolysis process,5-Mercapto-1-phenyl-1H-tetrazole not only acts as a sulfur source and reacts with nickel ions to form nickel sulfide nanoparticles in situ,but also its own nitrogen-rich structure provides a combination of nitrogen and sulfur.Doped with carbon skeleton.We have prepared Ni-PTA MOF samples at different temperatures by controlling the calcination conditions.When used as a negative electrode material for lithium-ion batteries,when the current density is 0.1A g-1,the capacity of the Ni S1.03@NSC600composite electrode remains at 1053.6 m Ah g-1 after 100 cycles.Even after 500 cycles at a current density of 1 A g-1,the reversible specific capacity remains at 400 m Ah g-1.This excellent electrochemical performance is because the hollow porous structure can be used as a protective layer to buffer the volume expansion of the electrode material caused by the insertion and extraction of lithium ions during the charging and discharging process,and the porosity is conducive to the full contact of the electrolyte.(4)Cobalt nitrate hexahydrate and 5-Mercapto-1-phenyl-1H-tetrazole are hydrothermally reacted to form a plate-shaped Co-PTA MOF,which is then used as a precursor to pyrolyze and vulcanize at high temperature to obtain a porous tube Cox S@NSC composite materials.By controlling the calcination conditions,samples at different temperatures were prepared.The results show that the Co1.097S/Co9S8@NSC600 composites is used as the negative electrode material for lithium-ion batteries.After 100 cycles at a current density of 0.1 A g-1,its reversible specific capacity remains at 668.4 m Ah g-1,which has good lithium storage performance.This excellent electrochemical performance is mainly due to the porous structure formed between the uniform and dense cobalt sulfide nanoparticles,which effectively promotes the full contact of the electrolyte.In addition,the cobalt sulfide nanoparticles embedded on the surface of the carbon skeleton enhance the conductivity of the electrode material.