Outstanding Lithium Storage Performance of a Copper-Coordinated Metal-Covalent Organic Framework as Anode Material for Lithium-Ion Batteries

Metal-covalent organic frameworks(MCOF)as a bridge between covalent organic framework(COF)and metal organic framework(MOF)possess the characteristics of open metal sites,structure stability,crystallinity,tunability as well as porosity,but still in its infancy.In this work,a covalent organic framework DT-COF with a keto-enamine structure synthesized from the condensation of 3,3'-dihydroxybiphenyl diamine(DHBD)and triformylphloroglucinol(TFP)was coordinated with Cu^(2+)by a simple post-modification method to a obtain a copper-coordinated metal-covalent organic framework of Cu-DT COF.The isomerization from a keto-enamine structure of DT-COF to a enol-imine structure of Cu-DT COF is induced due to the coordination interaction of Cu^(2+).The structure change of Cu-DT COF induces the change of the electron distribution in the Cu-DT COF,which greatly promotes the activation and deep Li-storage behavior of the COF skeleton.As anode material for lithium-ion batteries(LIBs),Cu-DT COF exhibits greatly improved electrochemical performance,retaining the specific capacities of 760 mAh g^(-1)after 200 cycles and 505 mAh g^(-1)after 500 cycles at a current density of 0.5 A g^(-1).The preliminary lithium storage mechanism studies indicate that Cu^(2+)is also involved in the lithium storage process.A possible mechanism for Cu-DT COF was proposed on the basis of FT-IR,XPS,EPR characterization and electrochemical analysis.This work enlightens a novel strategy to improve the energy storage performance of COF and promotes the application of COF and MCOF in LIBs.