Design,construction And Electrochemical Performances Of Transition Metal Oxide/Carbon Composites

The sustainable developments of the lithium ion batteries and sodium ion batteries are largely depend on the exploitation of new types of electrode materials with high specific capacity,excellent rate capability,and long life,especially cyclic stable anode materials.Conventional commercial graphite with relatively low theoretical capacity(372 mAh g^-1)may be hard to meet the tremendous demands of high-energy applications of lithium-ion batteries（LIBs）.Therefore,it is vital to explore new materials with high specific capacity,excellent rate capability,and long cycle life.Because of the high theoretical capacity,low cost and low toxicity,transition metal oxides（TMOs）are considered as promising anode materials for LIBs and SIBs.However,the poor cycling stability and inferior rate capability resulting from the large volume variation during lithiation/sodiation process and the intrinsic low electronic conductivity limit their further application.In order to solve the problems of TMOs,carbon-based metal oxide composites with complex structures derived from metal-organic frameworks（MOFs）have emerged as the promising electrode for LIBs and SIBs.In this article,we have synthesized the yolk-shell carbon-based Co₃O₄（Co₃O₄/C）dodecahedrons derived from zeolitic imidazolate frameworks ZIF-67.Modern testing technologies were utilized to characterize the structure of Co₃O₄/C in detail and probe its capacity of lithium/sodium storage.On the other hand,the zeolite imidazoleskeletonmetalcompoundcoatedmetaloxidecompounds（CoMn₂O₄/Co-ZIF,ZnO/Zn-ZIF and CoSn（OH）₆/Co-ZIF）were synthesized by a low temperature vapor deposition method.And their characterizations were detailedly described.And the electrochemical performances of CoO&MnO/C as the anode material of LIBs were tested.The main research results are as follows:（1）The ZIF-67 precursor was synthesized by a simple co-precipitated method.And then the hierarchical yolk-shell Co₃O₄/C dodecahedrons were prepared by a facile interface-modulated controlling the two-step heat treatment process.And it has a larger specific surface area of 179.4 m²g^-1.（2）When used as anodes for LIBs,the yolk-shell Co₃O₄/C dodecahedrons demonstrate a high specific capacity and excellent cycling stability(1100 mAh g^-11 after 120 cycles at 200 mA g^-1).Moreover,when used as the SIB anode,the composite displays an outstanding rate capability(307 mAh g^-1at 1000 mA g^-1and 269 mAh g^-11 at 2000 mA g^-1).（3）CoMn₂O₄/Co-ZIF,ZnO/Zn-ZIFandCoSn（OH）₆/Co-ZIFwere successfully synthesized by the low pressure vapor deposition method with CoMn₂O₄ nanowire,ZnO microflower and hollow CoSn（OH）₆ nanocube as the precursor,respectively.Then a series of test methods were used to prove the feasibility of this method for preparation of MOFs.CoMn₂O₄/ZIF was calcined by appropriate heat treatment,and then the ZIF compound coated on the surface was carbonized to obtain CoO&MnO/C.（4）When used as the LIB anode,the CoO&MnO/C exhibits 1200 mAh g^-1at the current density of 100 mA g^-11 after 200 cycles,and the capacity remains 720.5mAh g^-11 at 2000 mAh g^-1,indicating excellent cyclability and rate capability...