Preparation And Electrochemical Properties Of Mof Derived Bimetallic Sulfides

Metal-Organic Frameworks（MOF）is a typical porous material with a topological structure formed by coordination bond between metal ions as the center and organic ligands.With unique porous structure and high specific surface area,its derivatives are good precursors for the design and preparation of micro/nanostructured composite materials.Through the structural design and composition control of MOF precursor,the poor intrinsic conductivity and obvious volume effect of metal sulfide can be effectively solved,and the electrochemical performance of the material can be significantly improved.In this paper,the author used cobalt-based MOF（ZIF-67）as a precursor with the introduction of different metals to design multiple synthesis process,prepare bimetallic sulfides with various morphologies and structures,and conduct researches on their electrochemical performance.（1）Firstly,the precursor Zn Co-MOF was prepared,and phenolic resin was polymerized on the surface of MOF.Finally,the dodecahedron Co S/Zn S@NDC was prepared by high temperature vulcanization,and its lithium storage performance was studied by comparing with its single component.The results show that the specific discharge capacity of Co S/Zn S@NDC is 1105.3 m A h g^-1after 100 cycles at the current density of 0.1 A g^-1,indicating that the material has high cyclic stability.In addition,the effect of nitrogen double carbon coating on the electrochemical properties of the materials was investigated.The results show that the bimetallic sulfide coated with nitrogen doped double carbon shell has higher electrical conductivity and cycle stability.After 100cycles,Co S/Zn S@NDC has A discharge capacity of 279.5m Ah g^-1at 0.1A g^-1current density.Although it still performs electrochemically superior than the reference sample,further material optimization is required due to the higher ionic radius of the sodium ion.（2）In order to improve the comprehensive electrochemical performance of the material,molybdenum disulfide（Mo S₂）was used to modify cobalt-based MOF derivatives.Firstly,ZIF-67 was formed by simple co-precipitation at room temperature,and then Co S/NC was obtained by high temperature vulcanization.Finally,Co S/NC@Mo S2was successfully prepared by deposition of Mo S₂nanosheets outside the material through hydrothermal synthesis.The lithium storage performance of the prepared material is studied.Under the current density of 0.1A g^-1,the discharge specific capacity of 1241.4 m Ah g^-1can still be maintained after 100 cycles,and the coulomb efficiency is almost 100%,its cycle stability is far better than that of single component metal sulfide.The addition of sodium molybdate was then modified,and Co S/NC@Mo S₂of various metal ratios were created to test the pertinent electrical properties in order to investigate the contribution of various constituents to the material’s electrical properties.According to the findings,CMS-2,a suitable sodium molybdate,had greater cycle stability.In addition,the study on the performance of the material for storing sodium shows that the performance of the material is similar to that of lithium storage.Compared with the comparison sample,CMS-2 has better cyclic stability,capacity retention rate,charge transfer impedance and sodium ion diffusion coefficient.In order to further improve the electrochemical performance of the material,ZIF-L precursor was prepared by different synthesis conditions,and glucose solution was added during the preparation of Mo S₂to increase the layer spacing of Mo S₂to prepare metallic phase 1T-Mo S₂.Co₃S₄/NC@1T-Mo S₂was successfully prepared.Its electrochemical performance was tested.When used in LIB,the discharge specific capacity of 1192.2 m Ah g^-1could be maintained after 100 cycles at the current density of 0.1A g^-1.When used as SIB,the discharge specific capacity remained at 615.3 m Ah g^-1after100 cycles.It shows the excellent electrochemical properties of the material.（3）ZIF-67 was used as the sacrificial template,then nickel nitrate was added to etch,and the Ni/Co-LDH hollow nanocages were recombined on the surface of MOF precursor to form the layered Ni/Co-LDH hollow nanocages by ion exchange,and then Co S₂/Ni S₂composite was obtained by hydrothermal curing.The electrochemical performance of sodium ion battery anode material was tested.The initial discharge capacity was 936.8 m Ah g^-1at 0.1A g^-1current density,and the initial Coulomb efficiency was 78.6%.After 100 cycles,its specific discharge capacity is 704.1 m Ah g^-1,Coulomb efficiency is 99%,has a high capacity retention rate.In addition,Co S₂/Ni S₂also has a higher charge transport capacity and sodium ion migration rate in EIS and GITT tests.