Preparation And Sodium Storage Properties Of Coal-based Carbon Fibers

Sodium-ion batteries(SIBs)are expected to replace lithium-ion batteries for applications such as low-speed electric vehicles or large-scale energy storage systems,which can effectively alleviate the problem of insufficient lithium resources reserves.However,the lack of suitable anode materials for sodium ion batteries limits the development and application of sodium ion batteries.However,the lack of suitable anode materials for SIBs limits the development and application of SIBs.In this paper,carbon nanofibers were prepared by electrostatic spinning and high temperature calcination using coal from Xinjiang Kuche as raw materials.Porous coal-based carbon nanofibers and coal-based carbon fibers/tin were prepared by optimizing the preparation process and combining template method and chemical activation pore-making strategy.The correlation between the material structure,morphology and electrochemical properties of the material as an anode material for SIBs is studied.The main research contents are as follows:(1)Coal was treated with mixed strong acid(V_H2SO4:V_HNO3=1:3)to obtain oxidized coal(OC),and the porous coal-based carbon fibers were prepared by electrostatic spinning and calcination treatment with OC as carbon source and poly(methyl methacrylate)(PMMA)as pore-forming agent,studying the effects of adding different amounts of pore-forming agent on fiber structure and properties.After testing,it was found that the sample added with 0.4 g PMMA calcined at 750°C possesses better cycling stability and rate performance,and the reversible discharge capacity reaches 159.3 m A h g^-1 after 150 cycles at 0.1 A g^-1,and its capacity retention rate is 92%;the reversible discharge capacity is 132.8 m A h g^-1 after 1000 cycles at 1 A g^-1.The excellent electrochemical performance is attributed to the unique three-dimensional(3D)network framework composed of porous coal-based carbon fibers,which increases the electrical conductivity of the material,shortens the electron and Na⁺transport paths,and accelerates the reaction kinetics;meanwhile,the suitable specific surface area and well-developed pore structure of the material facilitate sufficient contact between the electrolyte and the electrode,and provide more active sites,which in turn enhance the electrochemical performance of the material.(2)Hierarchically porous coal-based carbon nanofibers(HPCCNFs)were prepared by electrostatic spinning method combined with chemical activation method using OC and polyacrylonitrile(PAN)as carbon sources,and the effect of activation time on the pore structure and properties of the fibers was investigated.The specific surface area test showed that the sample activated at 800°C for 1 h has a high specific surface area(S_BET=2236.43 m² g^-1)and a suitable micro-mesopore distribution,the sample exhibits excellent cycling stability and rate performance.As anode electrode material of SIBs,the material exhibits excellent cycling stability and rate performance.After 100 cycles at 0.1A g^-1,it still has a discharge capacity of 215 m A h g^-1 and its capacity retention rate is76%.At a higher current density(5 A g^-1),the discharge capacity is 109 m A h g^-1 after1000 cycles.The excellent electrochemical performance is attributed to the interwoven network framework that improves the electrical conductivity of the material and shortens the Na⁺and electron transport paths;the oxygen-containing functional groups on the material surface increase the active sites on the material surface;the appropriate specific surface area and the rich pore structure can increase the contact area between the electrode and the electrolyte,thus promoting the reaction kinetics.(3)The coal-based carbon fiber/tin composites were prepared by electrostatic spinning method and calcination treatment using OC and PAN as carbon sources and stannous chloride dihydrate(Sn Cl₂·2H₂O)as tin source.The effect of OC addition on the structure and properties of the material was investigated.The composites have excellent electrochemical performance when 0.4 g OC was added to the spinning stock solution.After 200 cycles at 0.1 A g^-1,the reversible capacity of 249.1 m A h g^-1 with a capacity retention rate of 96%;and the reversible capacity of 175.6 m A h g^-1 after 500 cycles at 1A g^-1 are obtained.The excellent electrochemical performance is attributed to the one-dimensional nanofiber network structure that not only increases the electrical conductivity of the composite,but also allows the active material to be in full contact with the electrolyte with no"dead volume",resulting in an efficient electron/ion transport system;the ultra-small Sn nanoparticles are uniformly embedded in the coal-based carbon fiber matrix,which effectively avoid serious volume changes of Na⁺during charge/discharge process.