Study On Preparation Of Sb-based Carbon Nanofibers And Their Performance As Anode Material For Sodium Ion Batteries

Lithium-ion batteries are widely used in electronic equipment,electric vehicles and other fields due to their high energy density,long cycle stability and no memory effect.However,the reserves of lithium resources on the earth are difficult to meet the future demand for lithium ion batteries.Sodium ion batteries have a similar reaction mechanism to lithium-ion batteries.At the same time,sodium resources are abundant and cheap,so it is considered as the most potential substitute for lithium-ion batteries.However,due to the large ionic radius of sodium ions,the ionic kinetic reaction is slow,so it is necessary to find a suitable anode material for sodium ion battery.Alloy materials can be used as anodic materials for sodium ion batteries because they can form alloying phase with sodium.The theoretical capacity of antimony element is as high as 660 m Ah g^-1.However,the large volume expansion in the cycle process causes the agglomeration of antimony particles,resulting in poor cycling performance.The agglomeration of antimony particles induced by volume expansion can be alleviated by reducing particle size and coating with carbon-based materials.In recent years,the reversible conversion reaction between Sb₂O₃ and Sb has been proved in sodium ion batteries,which makes Sb₂O₃ as the anode of sodium ion batteries have a theoretical capacity of up to 1103 m Ah g^-1,but the poor electrical conductivity limits its electrochemical performance.Electrospinning is a simple and mature method to synthesize carbon fiber.Through the method of electrospinning,we can easily achieve uniform alignment of alloy materials and carbon fiber.Meanwhile,through the pre-oxidation treatment and carbonization treatment of the spinning precursor,we can realize the synthesis of flexible carbon fiber composites,to meet the needs of future flexible devices.We have successfully synthesized a flexible composite carbon nanofiber(Sb/Sb₂O₃@NCNFs)with Sb and Sb₂O₃ heterojunction by electrospinning and carbothermal reduction.Sb/Sb₂O₃nanoparticles embedded in carbon fibers can effectively inhibit the volume expansion during the Na alloy/dealloying reaction.At the same time,one-dimensional nanofibers can realize fast Na⁺transport.The precursor nanofibers can be synthesized by cheap electrospinning.Then carbonization to get Sb/Sb₂O₃@NCNFs film.Sb/Sb₂O₃@NCNFs film can be directly used as an independent electrode,which can reduce the influence of conductive agent,binder and metal collector on the electrode and reduce the cost of the battery.In addition,our results also show that the flexible free-standing Sb/Sb₂O₃@NCNFs electrode,as the anode of the sodium ion battery,exhibits excellent electrochemical performance with high specific capacity and excellent cycle stability(reaching 527.3 m Ah g^-1 after 100 cycles at a current density of 0.1A g^-1).MXenes,a novel kind of 2D layered transition-metal carbides or nitrides,has excellent electrical conductivity and is beneficial to the migration of sodium ions.A few layers of V₂CT_x Mxene powder were uniformly dispersed in the spinning solution containing Sb Cl₃ and PAN.After stabilization and carbonization treatment,a small amount of V₂CT_x MXene doped Sb composite nanofibers were successfully synthesized.The composite fibers were characterized by XRD,SEM and TEM,and the results showed that MXene and Sb nanoparticles were uniformly distributed in the carbon fibers.The materials were made into electrodes and assembled into sodium ion batteries for electrochemical testing.The addition of MXene enhances the electrical conductivity of the material,which enables the material to have excellent rate performance.The capacity of the material can still reach up to 300 m A h g^-1 at the current density of 1A g^-1,which can meet the needs of fast charging under large current currents.