Lithium Storage Performance Of Sn/SnO₂-based Carbon Nanofibers Anode Prepared By Electrospinning

Flexible wearable electronic devices continue to promote the development of flexible lithium-ion battery,electrode is the key component of the battery.The flexible electrode is of great significance to the development of flexible lithium battery.Self-standing electrodes have been used in lithium-ion batteries because they do not need binders,conductive agents and efficient and simple preparation methods.Tin based and tin oxide based composite carbon materials have become one of the potential development directions of self-supporting electrode materials because of their high theoretical capacity and stable potential platform.However,the cycling stability of Sn based and SnO₂-based anodes is poor,and the specific capacity and rate performance decrease seriously after many cycles.The main reason is the volume expansion of active particles in the process of charging and discharging to insert and remove lithium ions,resulting in huge internal stress,which leads to the crushing of active materials.At present,there are three ways to improve the cycling performance and rate performance of tin based self-supporting anode,including reducing the size of active particles,compounding with carbon materials and constructing unique nanostructures.The effectiveness of the above strategies has been proved,but few studies have focused on the preparation of excellent self-supporting electrode by modifying the interface between the active material and electrospinning solution,and few studies have focused on the lithium storage performance of aligned carbon nanofiber composite SnO₂ anode.Based on this,the main works of this paper are as follows:（1）Based on electrospinning technology,tin oxide particles and polyacrylonitrile were used as the main raw materials.Ionic liquid（1-allyl-3-methylimidazolium chloride）was used to modify the interface between tin oxide particles and electrospinning solution.Tin oxide was pyrolyzed at high temperature and reduced at the same time to prepare super uniform Sn particle composite porous carbon nano-fibers self-supporting electrode（Sn@MCNFs-IL）.The results show that the tin nanoparticles modified by ionic liquid are more evenly dispersed in the precursor solution of electrospinning.The cation of ionic liquid is bonded with SnO₂ to improve the surface properties of SnO₂ particles.Ionic liquids increase the conductivity of electrospinning solution.The high conductivity and Ultra-uniform electrospinning solution ensure the Ultra-uniform tin oxide embedded in carbon nanofibers.Sufficient buffer space and larger lithium storage surface area improve the specific capacity and cycle life of the electrode;The volatilization of ionic liquids in the pyrolysis process leads to the introduction of more pores on the surface of carbon nanofibers to construct porous carbon nanofibers,which further improves the transfer speed of ions and electrons,thus reducing the mass transfer resistance of the electrode.（2）Tin oxide composites aligned carbon nanofiber self-supporting electrode（SnO₂@ACNF）was prepared by electrospinning technology at high speed rotation of collecting drums.The aligned carbon nanofiber cushion is loaded with active lithium storage particles and takes the role of collecting fluid,and directly contacts with electrolyte.The surface morphology and three-dimensional structure affect the ability of electrolyte to infiltrate it,the load of active particles and the conductivity of electrode structure.The results show that the active particles of tin oxide are more evenly dispersed and embedded in the network structure of aligned carbon nanofibers,and the surface of nanofiber mats is smoother,which improves the specific capacity of electrodes and the Coulombic efficiency,and stabilizes the solid electrolyte boundary film.The structure of three-dimensional orderly stacking and two-dimensional plane orientation arrangement can reduce the electrode resistance,and its adequate spaces can alleviate the particle volume expansion stress and ultimately improve the cycling performance of lithium battery.