Preparation And Electrochemical Properties Of Fluorine-doped Nitrogen-rich Carbon-based Nanofibers

The contradiction between the increasing energy demand of the people and the unevenly distributed and limited fossil fuel resources on the earth has become increasingly prominent,so the development of new energy storage devices is urgent.Lithium-ion batteries(LIBs)have been used in various applications due to their long life-span,high specific energy density,low self-discharge rate and no memory effect.However,the uneven distribution of lithium resources and the foreseeable and increased price prompted researchers to find new energy storage.As a low-cost alternative to LIBs,sodium ion batteries(NIBs)have attracted much attention due to their similar electrochemical properties to LIBs,high sodium crust abundance and low cost.However,their development still faces munch challenges such as poor cycle stability and poor rate performance.In addition,the binder of traditional electrodes is usually used to combine a single active material with a conductive additive.The binder is usually electrochemically inert and insulating,which reduces the total energy density of the battery and leads to poor cycle stability.Therefore,binder-free/flexible electrodes provide huge opportunities for high-performance NIBs in terms of improving electronic conductivity and reversibility of electrochemical reactions.Electrospinning is an effective method to prepare flexible nanofibers with large surface area and controllable morphology.In this work,we first prepare nitrogen-rich carbon nanofibers(NCNFs)by electrospinning,which can increase the conductivity of carbon materials and create more active sites,thereby increasing the storage capacity of sodium.Then,NCNFs are treated by plasma fluorination to obtain nitrogen-rich carbon nanofibers(PFNCNFs)with abundant semi-ionic C-F bonds,which can accelerate the transfer of electrons and ions in the electrode material and improve the long-cycle stability of NCNFs.Based on the study of PFNCNFs nanomaterials obtained by uniaxial spinning,we use coaxial spinning to embed Sn O_x nanoparticles in NCNFs to obtain carbon-coated amorphous Sn O_x nanofibers(Sn O_x@C),and the carbon nanofibers are used as the shell to buffer the volume swell of alloy nanoparticles while providing good electrical conductivity.Finally,the Sn O_x@C is treated by plasma fluorination to obtain Sn O_x@C nanofibers(PF-Sn O_x@C)with enriched semi-ionic C-F bonds.This work carefully studied the morphology,electrochemical performance and reaction mechanism of NCNFs,Sn O_x@C and PF-Sn O_x@C composites.It is found that the flexible nanofiber anode materials used for NIBs have ultra-stable long-cycle performance and good rate performance by various technical researches.Therefore,this work shows that plasma treatment of electrospun nanofibers has great potential in the synthesis of NIBs anode materials.