Preparation And Lithium Storage Properties Of Silicon Modified Iron-Based Metal Organic Frameworks

With the intensification of the global energy crisis and the greenhouse effect,the improvement of the performance of energy storage devices has received increasing attention.As the most widely used energy storage device,the performance of lithium-ion batteries has been difficult to meet the needs of the world today.The reason is that the theoretical capacity of traditional anode materials for commercial lithium-ion batteries is low.In order to improve the battery capacity,it is an effective way to develop materials with better performance.Among many candidate materials,composites with the unique frame structure and porous structure derived from heat treatment of metal-organic frameworks have attracted extensive attention from researchers.In this paper,a composite material for lithium-ion battery anode was prepared through the study of iron-based MOF and the use of silicon materials to modify it.The specific research contents include:（1）Fe₃O₄@C-100 and Fe₃O₄@C-101 composites with the porous structure were prepared by co-precipitation method and solvothermal method using MIL-100（Fe）and MIL-101（Fe）as self-sacrificial templates,and their electrochemical properties were compared.The results show that the discharge-specific capacity of Fe₃O₄@C-101 composite reaches 1298.5 m Ah/g after 300 cycles at a current density of 1 A/g,which is better than 853.5 m Ah/g of Fe₃O₄@C-100.The electrochemical properties of both are much better than pure Fe₃O₄.The excellent performance of the two composites shows that the composite material derived from MOF guarantees the high electronic conductivity and ionic conductivity necessary for rapid charge and discharge with its stable structure,which provides a new idea for the structural design of electrode materials.（2）Si/Fe₃O₄@C composites were prepared by solvothermal method combined with heat treatment.The results show that the material still has a reversible specific capacity of 1617m Ah/g after 200 cycles at a current density of 0.2 A/g.Its excellent electrochemical performance shows that the incorporation of Si materials into the structure of high-porosity MOF derivatives can effectively alleviate the volume effect of Si materials.At the same time,it combines the advantages of the high theoretical capacity of silicon materials and metal oxide materials,which has reference value for the development of higher-performance anode materials.（3）Fe₃O₄@C@SiO₂ composites with the core-shell structure were prepared by coating MIL-101（Fe）with silica produced by hydrolysis of tetraethoxysilane and heat treatment.It was applied to the anode of Lithium-ion battery,and 80%of the initial capacity（428 m Ah/g）was maintained after 2000 cycles at a current density of 5 A/g,showing excellent cycle stability.The protective and supporting effects of the silica shell further improve the cycle stability of MOF derivatives,making Fe₃O₄@C@SiO₂ composites have practical application prospects.