Synthesis Of Metal Organic Framework Derivatives And Their Applications In Lithium-ion Batteries

Due to reduce and global pollution caused by burning of fossil fuels,energy consumption in the world is becoming more serious,energy demand has become more urgent,in order to reduce fossil fuel consumption and climate related problems,environmental protection way of producing electrical energy such as hydroelectric,solar,wind and other renewable energy arises at the historic moment.For rational utilization and regulation,researchers are committed to the development and application of electrochemically efficient energy storage and conversion green technology.Fortunately,the invention of rechargeable batteries has made green,sustainable ways of supplying electricity possible.Lithium-ion batteries(LIBS)have the advantages of good stability,high energy density,large reversible capacity,long service life,etc.,which is considered as one of the major breakthroughs in the field of electrochemical efficient energy storage in recent decades.It has also become the main power source for portable electronic products and new energy vehicles.It is well known that electrode materials used in battery structures play a crucial role in their electrochemical performance,and the research in this area has become the focus of attention.Up to now,the traditional graphite anode material has been widely used in lithium ion batteries,but due to its limited capacity,it can not meet the increasing demand for energy storage applications.In contrast,transition metal oxygen/sulfide and its carbon composites exhibit high theoretical specific capacity and are considered as promising electrode materials.Transition metal oxide/sulfide and its carbon composites derived from metal organic framework have strong competitiveness in many anode materials for lithium-ion battery due to their porous properties.Based on ZIF-67,three kinds of composite materials were synthesized.Besides the synthesis and characterization of the experimental materials,the performance of the materials was tested by analysis software.The specific work is as follows:(1)Synthesis of Co₃O₄/CoMoO₄composites and their properties in lithium ion batteriesPorous Co₃O₄/CoMoO₄composites were synthesized by in-situ growth of a polyoxometalate(POM)on ZIF-67 by solution-thermal method.POM@ZIF-67 was synthesized and calcined at high temperature in O₂atmosphere.The microstructure and morphology of the composites were studied by XRD,SEM and EDS.It is found that the diamond polyhedron structure of ZIF-67 can be maintained stably in the composites before calcination,but the homogeneous doped phase of Co and Mo is due to the collapse of ZIF-67 skeleton structure and the oxidation of cobalt to Co₃O₄.When the lithium ion battery adopts Co₃O₄/CoMoO₄as the anode material,the battery exhibits high lithium storage capacity(1252.3 m Ah g^-1at 100 m A g^-1),high cycle stability(89.6%capacity retention after50 cycles)and good rate performance.The experimental results show that Co₃O₄/CoMoO₄composites have been greatly improved in cycling and multiplying properties as well as electrochemical properties compared with Co₃O₄and CoMoO₄composites.(2)Synthesis of Co₃O₄@rGO composite materials and its performance in lithium ion batteriesAiming at the poor electrochemical properties of Co₃O₄,the lamellar Co₃O₄@rGO composite was prepared by solution-thermal method,using graphene oxide(GO)as matrix,modifying ZIF-67 in situ on the surface of Co₃O₄,and then calcined at high temperature in O₂atmosphere.By means of XRD and SEM,the morphological characterization of the composites was studied.It was found that the layered structure of graphene was well preserved and the nanoparticles were uniformly distributed.Compared with pristine Co₃O₄material,Co₃O₄@rGO composite material as anode material of lithium-ion battery has been improved greatly in the aspects of cycling performance and magnification performance.(3)Synthesis of CoS₂@rGO composite materials and its performance in lithium ion batteriesCoS₂composites(CoS₂@rGO)were successfully synthesized by hydrothermal synthesis,N₂ atmosphere heat treatment and hydrothermal treatment with secondary introduction of sulfur.The results of XRD and SEM analysis showed that the CoS₂ particles were uniformly distributed on the surface of reduced graphene oxide.CoS₂@rGO cyclic performance and rate performance are greatly improved compared to pristine CoS₂ material.