Preparation And Properties Of FeF₃/C Nanocomposites For Sodium-Ion Storage

The ferrofluoride electrode material based on the electrochemical conversion reaction mechanism has a higher theoretical specific capacity than the cathode material of the conventional intercalation reaction mechanism.However,the electrochemical performance of the material is seriously affected by the poor electrical conductivity and the sluggish electrochemical kinetics of the fluorinated iron electrode material.For these problems with fluorinated iron electrode materials,we carried out the strategy that the ferro fluoride nanoparticles were in situ embedded in the conductive carbon substrate,the amorphous FeF₃/MOF carbon nanocomposites and the amorphous FeF₃/3D graphene analogue carbon nanocomposites were successfully synthesized by this strategy.The phase of the composites was characterized by XRD,and the morphology of the composites was characterized by SEM and TEM.The carbon content and carbon properties of the composites were determined and analyzed by TGA and Raman tests.The XPS test was used to analyze the surface characteristics of the material and to determine the elements of the material and its chemical valence.Finally,the electrochemical properties of the materials were tested by constant current charge/discharge test,CV test and other electrochemical test methods.We found that the materials we produced showed excellent modification effect.In detail,our work were carried out from the following two aspects:1.amorphous Fe F₃/C nanopaticles composited with graphitized porous branch-like carbon framework have been successfully fabricated from the precursors of uniform Fe-MOFs nanocrystals by the carbonization process and the gas-solid fluorination reaction process.Compared with other materials with different carbonization condition in this work,the FeF₃/C-700-3h nanocomposites exhibit exceptional electrochemical performance with a high sodium ion storage capacity(302.2 mAh g^-1)at low current density,an excellent rate performance at up to current density of 1500 mA g^-1,and good capacity retention over 100 cycles.The outstanding electrochemical features of the FeF₃/C-700-3h nanocomposites are attributed to its amorphous structure and high-graphited porous carbon framework,which is in favor of the ionic and electronic transport and the reaction kinetics of electrode materials.This work is expected to be useful for other energy storage materials.2.The amorphous FeF₃/3D graphene analogue carbon nanocomposites was prepared by the gas-solid fluorination reaction process.And its precursor was synthesised by the auxiliary chemical blowing of iron nitrate and the carbonization of polyvinylpyrrolidone?PVP?at high temperature.amorphous iron fluoride nanoparticles are encapsulated in the porous carbon skeleton of the 3D frame carbon sheet in this composites.The electrochemical properties of the amorphous Fe F₃ composites with graphite carbon skeleton show excellent electrochemical performance.At a low current density of 20 mA g^-1,the first discharge capacity exceeds 175.1 mAh g^-1.And the materials exhibit a excellent rate performance at up to current density of 1000 mA g^-1.The excellent cycling stability of amorphous FeF₃/3D graphene analogue carbon nanocomposites is not only attributed to micro-nano-size,but also to the unique hollow three-dimensional graphene carbon framework.