The Preparation And Electrochemical Energy Storage Of Cobalt-based MOF Composites

With the increasingly severe energy shortage and environmental pollution,the search and development of innovative,efficient and environmentally friendly electrochemical energy storage system has become a research hotspot in recent years.In order to develop high-performance energy storage systems,researchers are committed to researching various types of new electrode materials.Compared with traditional carbon materials,cobalt-based composites have been widely used in energy storage because of their excellent theoretical specific capacity,good electrical conductivity and stable mechanical properties.In this paper,cobalt-based MOF composites were prepared by using metal-organic framework compounds?MOFs?as the starting point and cobalt as the building unit.The energy storage performance of MOFs as electrode materials in lithium-ion batteries,lithium-sulfur batteries and sodium-ion batteries was investigated.The prepared cobalt-based materials were characterized systematically and their electrochemical properties were studied.The main work can be divided into the following three parts:1.Cobalt-based MOF?Co-MOF?was directly loaded on three-dimensional graphene?3DGN?by solvothermal method.CoS₂ with N-doped carbon coating sheets anchored on3DGN?CoS₂-N-C/3DGN?was prepared by carbonizing and vulcanizing the precursor material?Co-MOF/3DGN?.The electrochemical performance of CoS₂-N-C/3DGN is better than that of pure CoS₂-N-C when it is used as the anode material of lithium ion batteries.When the current density is 100 mA g^-1,the reversible capacity of 409.5 mA h g^-1 can be maintained after 100 cycles.Such excellent cyclic stability is mainly attributed to the efficient synergistic integration of CoS₂-N-C and 3DGN.2.Co,Zn-ZIF was used as precursor,and silica was uniformly coated on Co,Zn-ZIF surface to synthesize core-shell structure of Co,Zn-ZIF@SiO₂,high temperature calcination treatment in nitrogen atmosphere and subsequent etching,cobalt and nitrogen co-doped carbon nanocomposites?Co-N-C?were obtained.As the cathode material of lithium-sulfur batteries,when the sulfur loading is 60%,the current density is 0.5 C,the stable capacity of the electrode material can reach 583.1 mA h g^-1 after 100 cycles,and the discharge capacity can still be maintained at 522.7 mA h g^-1 after 200 cycles.The more prominent electrochemical properties of the composite can be attributed to the doping of cobalt and nitrogen atoms with high conductivity and the hollow structure of yolk-shell.3.CoS₂ nanoparticles embedded in nitrogen-doped carbon nanosheets?CoS₂/NC?were designed and synthesized using Co-MOF as precursor,pyrolysis in nitrogen atmosphere and subsequent sulfurization reaction.When it is used as the anode material of sodium ion batteries,the electrode material exhibits better electrochemical performance.At the current density of 200 mA g^-1,the reversible capacity of 332 mA h g^-1 remains after 60 cycles.In addition,the discharge capacity can still display 326.6 mA h g^-1 at high current of 2000 mA g^-1.The composite exhibits good sodium storage performance,which is due to the synergistic effect of cobalt disulfide nanoparticles and nitrogen-doped carbon skeleton.