Lithium Storage Properties Of Amino Functionalized MOFs Derived Composites

Lithium-ion batteries（LIBs）are ideal electrochemical energy storage device of renewable energy sources by virtue of high energy density,long cycle life,low self-discharge,no memory effect and environmental benignity.The development of LIBs is of great significance to solve the energy crisis,cope with climate change and promote sustainable development.However,the traditional LIBs with commercial graphite as anode materials can hardly meet the ever-increasing power-supply requirements in terms of energy density and safety.Therefore,it is urgent to develop new anode materials with high energy density and safety.Iron-based compounds are considered as a promising candidate for next generation anode materials of LIBs due to its high theoretical capacity,moderate operating potential,abundant resources.Unfortunately,iron-based compounds suffer from poor electronic conductivity and low Coulombic efficiency,which make its large-scale application still a challenge.Considering the intrinsic problems of electrode materials,amino functional MOFs were used as precursors.The electrochemical performance was improved by means of interface regulation,structure design and carbon material composite.The specific research contents and results are as follows:（1）Amino-functionalized metal-organic framework of NH₂-MIL-101（Fe）was synthesized by the solvothermal method.As the functional group,-NH₂gives NH₂-MIL-101（Fe）a positive charge on its surface,which enables it to combine with negatively charged materials through electrostatic interaction,thus regulating the morphology and structure of the composite material.After pyrolysis in an inert atmosphere,it can retain the porous structure of MOFs and form the N-doping effect,which improve the electron and ion transport of the electrode materials.Therefore,NH₂-MIL-101（Fe）is a potential functional precursor of anode materials for LIBs.（2）The graphene-wrapped porous Fe₃O₄/N-doped C frameworks was fabricated by a MOF-derived strategy coupled with an electrostatic interaction induced self-assembly process（Fe₃O₄/NC@r GO）.NH₂-MIL-101（Fe）is spatially confined in graphene oxide（GO）by electrostatic interaction.After pyrolysis,graphene acts as a continuous conductive network and completely encapsulates Fe₃O₄/NC frameworks,promoting the formation of a stable solid electrolyte（SEI）film and maintaining the structural integrity of the electrode.The hierarchical porous structures of Fe₃O₄/NC@r GO not only improve diffusion kinetics,but also alleviate volume expansion.In virtue of the unique structure engineering,the as-built electrode exhibits an enhanced cycling stability(441 mA h g^-1 after 800 cycles at 2.0 A g^-1)and excellent rate capability(370 mA h g^-1 at 8.0 A g^-1).（3）Based on interface regulation strategy,the porous structures with strongly coupled FeP nanocrystals and N-doped carbon framework,which were anchored onto CC firmly were synthesized（FeP/NC@CC）.The carbon cloth was acidified to obtain surface oxygen-containing functional groups.The NH₂-MIL-101（Fe）with positive surface charges was in-situ grown on the surface of oxidized CC through a facile solvothermal method.The strong interfacial interaction not only drives the nucleation and growth process on the surface of oxidized CC,but also avoids the severe debonding of active materials.When used as binder-free flexible anode for LIBs,the three-dimensional hierarchical FeP/NC@CC architecture delivers ultrahigh reversible areal capacity of 5.8 mA h cm^-2 at 0.15 mA cm^-2 with high initial Coulombic efficiency up to 80.5%and extraordinary rate capability up to 6.0 mA cm^-2 with a reversible areal capacity of 2.0 mA h cm^-2.Moreover,the full cell fabricated with the FeP/NC@CC as the anode and Li FePO₄ as the cathode also exhibits excellent cycling stability of 0.5 mA h cm^-2 retention after 200 cycles at 0.5 mA cm^-2.