Synthesis And Lithium Storage Of Imine Covalent Organic Frameworks

In the new energy system,lithium-ion battery(LIBs)plays an important role.At present,inorganic transition metal oxides and phosphates are mainly used as electrode materials of LIBs.Transition metals mentioned above,such as Co and Ni,are non-renewable resources.In the long run,human development will face a serious shortage of resources.Therefore,the development of low-cost,high electrochemical energy,sustainable development of green LIBs electrode materials.In recent years,there have been reports about COFs as anode materials for LIBs.This paper mainly through the design and synthesis of different imines COFs,by adjusting and controlling the structure,aperture and active site of the material,to achieve its long cycle,high chemical stability,high specific capacity of lithium storage anode material preparation.(1)In this study,a COFs of imines with multiple active sites was synthesized by solvothermal method.The unique regulation of lithium-ion content of this material was achieved by introducing functional groups with reversible redox active hydroxyl and carbonyl groups into the pore wall of COFs.As a cathode material,it has excellent electrochemical properties.After charging and discharging cycles at the current density of 0.1 Ag^-1,its reversible specific capacity is stable at 764.1 m A hg^-1.After charging and discharging cycles for 8000times at the current density of 5.0 Ag^-1,its specific capacity is stable at 764.1 m A hg^-1.It still maintains a high reversible specific capacity of 156.3 m A hg^-1(almost 100%Coulomb efficiency and 63%total capacity retention rate).The results show that more reversible redox active sites introduced into the COFs material can improve the lithium storage performance of the material,showing its excellent electrochemical performance as a battery anode material,providing a new idea for the development of LIBs anode material.(2)In this study,COFs of different thicknesses were prepared on carbon nanotubes(CNTs)by in-situ fabrication method as anode materials for LIBs.Compared with pure COFs as anode material,its electrochemical performance is better.The experimental results show that:COF@CNTs anode materials have excellent electrochemical properties,among which,the reversible specific capacity of COFs with a few layered structures on the surface of COF@CNT-2 composite is 570 m A hg^-1 after charge-discharge cycles at the current density of 0.1 Ag^-1,After 2000 charge-discharge cycles at a current density of 1 Ag^-1,it still has a large reversible specific capacity of 373 m A hg^-1 and a Coulomb efficiency of nearly 100%,which is comparable to most previously reported COFs anode materials.Doping CNTs conductive materials can shorten the ion/electron diffusion channel distance and improve the conductivity and structural stability of the composites,which makes some contributions to improve the electrochemical performance of the composites as anode materials for LIBs.