Preparation And Electrochemical Performance Of Bismuth-based Metal Organic Frame Anode Materials

As the heart of our digital life,the graphite anode of commercial lithium-ion batteries has many disadvantages,such as low specific capacity,poor rate performance,and potential safety hazards.Based on these problems,we designed and prepared a variety of Bi-based composite materials using Bi-MOFs as precursors.The product was characterized and observed by X-ray diffraction technology and electron microscopy technology.Then The electrochemical performance of the composite material was tested.The specific research content is as follows:(1)Bi@C composites are prepared by carbonizing Bi-MOFs by calcination method.By changing different reaction temperatures to control the morphology of the materials,the corresponding products also exhibit different electrochemical properties.The test results show that the Bi@C-700 obtained when the calcination temperature is 700?has the best lithium storage performance,and it maintains a specific capacity of 305 m Ah g^-1even after 500 cycles at a current density of 1 A g^-1.(Coulombic efficiency is above 99%)When the current density is increased to 5 A g^-1,the bismuth/carbon composite material still has a capacity of 150 m Ah g^-1 proving the energy storage potential of this structure.(2)Bi-MOFs are mixed with reduced graphene oxide and then calcined,and Bi@C@RGO-700mile is prepared by high-energy mechanical ball milling.The electrochemical test results show that its negative electrode performance is stronger than that of pure carbon-coated products.At a current density of 1 A g^-1,the material still maintains a specific capacity of 380 m Ah g^-1 after 500 cycles,and also has an excellent performance in the rate performance test.At a current density of 0.1 A g^-1,the specific capacity of the material is 514 m Ah g^-1.When the current density increases to 5 A g^-1,it still maintains 253 m Ah g^-1.In addition,we analyzed the lithium ion storage capacity contributed by different control processes in the material before and after ball milling by cyclic voltammetry,and found that the composite material after ball milling has a higher proportion of pseudocapacitance(88.8%vs.65.5%),indicating that the lithium storage process of the material is less controlled by diffusion.This phenomenon is attributed to its smaller particle size,which is conducive to faster lithium ion transmission.(3)Using the hydrothermal method to combine Bi-MOFs with reduced graphene oxide can make large pieces of reduced graphene oxide form a conductive substrate between Bi-MOFs,so that the active sites can be fully utilized.When the amount of reduced graphene oxide is 15 mg,the composite exhibits excellent lithium storage performance.After 500 cycles at a current density of 1 A g^-1,the specific capacity is 800m Ah g^-1.The part that exceeds the theoretical capacity of Bi is attributed to the synergistic effect of Bi-MOFs and reduced graphene oxide.Bi-MOFs are rich in a large number of oxygen-containing functional groups,providing considerable lithium storage sites,and the poor conductivity of Bi-MOFs themselves makes it impossible to effectively and reversibly store lithium.However,the presence of reduced graphene oxide improves this problem and enables the composite material to obtain excellent electrochemical performance.