Design Preparation And Performance Of Anode Of Sodium-ion Batteries Based On Tin Oxide/graphene Composite Nanostructure

With the increasing consumption of fossil fuels and environmental problems,the search for new environment-friendly energy storage technologies is particularly important.Sodium-ion batteries?SIBs?are abundant as substitutes for lithium-ion batteries?LIBs?and are increasingly popular in low prices.Unfortunately,due to the limitation of the radius of Na⁺ions,commercial graphite(LIBs:372 m Ah g^-1)does not provide a satisfactory sodium storage capacity.Therefore,it is particularly urgent to develop new electrode materials with excellent electrochemical properties for SIBs.Based on this,the environment-friendly Sn O₂ is widely studied as electrode material,combined with theoretical capacity(667 m Ah g^-1),and great electrochemical windows.However,in addition to volume expansion and low conductivity problems,Sn O₂ has its own insurmountable problems:?1?Na₂O?Sn O₂+4Na⁺+4e^-???Sn+2Na₂O?formed by the conversion reaction can prevent agglomeration and accommodate the associated volume expansion.However,phase separation and self-aggregation of the Sn and Na₂O interfaces significantly reduce the reversibility of the reaction thus leading to the large irreversible capacity loss and low initial coulombic efficiency?CE?.?2?The self-aggregation during the cycle causes the gradual coarseness of the Sn particles or the cluster further hinders the diffusion of Na⁺in subsequent alloy reactions?Sn+x Na⁺+xe^-???Na_xSn?.In view of the above problems,this paper first constructed the Sn O₂@Sn/nitrogen doped graphene aerogel?Sn O₂@Sn/NGA?of the core-shell structure by a microwave plasma process.During the initial discharge cycle,the material obtained a stable Na₂O@Sn interface,which greatly improved the reversibility of the conversion reaction.At the same time,the thinner Na₂O layer can not promote the diffusion of Na⁺,but also effectively prevent Sn particles from reuniting.Moreover,the plasma also improves the quality of NGA,reduced the content of the oxygen containing functional groups in graphene oxide and improved the degree of graphitization and electrical conductivity.Based on these advantages,Sn O₂@Sn/NGA performs excellent sodium storage as electrode material.On this basis,this paper uses hydrogen atmosphere thermal annealing to prepare the ternary material Sn O_x-Sn/NGA,which proves that the microwave plasma is key to form the core-shell structure.On the other hand,for the traditional electrode,binders are often used to bond active materials.Unfortunately,overall energy density is reduced by binders which lead to poor cycling stability owing to its electrochemical inactivity and insulation.Therefore,the Sn O₂/3DNG foam is prepared by ice template method.The pores and channels in 3DNG can not only help electrolyte immersion and ion diffusion,but also accommodate the volume expansion of Sn O₂.As a result,the Sn O₂/3DNG electrode delivers a specific capacity of 497 m Ah g^-1 at 50 m A g^-1.