Preparation And Sodium Storage Performance Of Titanium-based Anode Materials By Electrospinning

In recent decades,lithium-ion batteries?LIBs?have played an important role in everyday life?such as electric/hybrid vehicles and portable electronics?due to their high energy density and long service life.However,disadvantages of limited lithium resources and high cost limit the commercial application of lithium batteries in the field of large-scale energy storage.In contrast,sodium-ion batteries?SIBs?are more suitable for low-cost energy storage equipment due to their rich sodium content and low price,which has attracted the attention of researchers at home and abroad.Among many sodium ion battery anode materials,titanium-based materials have been extensively studied due to their low cost,green non-toxicity and the like.However,titanium-based materials have wide band gaps,poor electronic conductivity,and low specific capacity,which limits their development and application in the field of sodium ion batteries.In this dissertation,through the techniques of structural design,compoundingand doping,the aim is to improve the cycle performance and large rate performance of titanium-based anode materials.And the primary research tasks are as follow:?1?Firstly,anatase TiO₂ nanofibers were synthesized by electrospinning and calcination,and then reacted with sodium hydroxide solution by hydrothermal method to form Na₂Ti₃O₇/C fluffy composite nanofibers?Na₂Ti₃O₇/C FNFs?.The results show that the Na₂Ti₃O₇/C FNFs with special structure exhibit high specific surface area,which makes full contact with the electrolyte,shortens the Na⁺/e^-transmission path,and significantly improves the material's large rate performance.The galvanostatic charge-discharge test shows that there is still 110 mAh g^-1 after 500cycles at 1 C(177 mA g^-1).Even at a high current density of 50 C,the discharge capacity was 58 mAh g^-1 with no capacity attenuation even after 1500 cycles,showing excellent large rate performance.?2?In order to improve the specific capacity of anatase TiO₂,a novel TiO₂-Sn composite nanofibers?TiO₂-Sn/C NFs?were prepared by a simple electrospinning technique.Due to the synergistic effect of a small amount of metal Sn and TiO₂,the TiO2-Sn/C NFs material has the advantages of stability of TiO2 and high specific capacity of Sn.Not only does the capacity of the material increase,but the presence of metallic Sn nanoparticles significantly improves the electrical conductivity of the composite.In addition,a study on the different composite amounts of Sn found that the electrochemical performance of TiO₂-Sn/C NFs-1 with 0.1 g SnCl₂·2H₂O was the best.It has a capacity of up to 190.8 mAh g^-1 after cycling 1000 times at a current density of 1 A g^-1,and the capacity retention rate is 94.5%,demonstrating excellent cycle performance.The material also exhibited excellent rate performance with discharge capacities of 214 and 147 mAh g^-1 at 0.5 and 4 A g^-1,respectively.?3?In order to further improve the conductivity of the anatase TiO₂ electrode material,nitrogen-doped carbon TiO2 composite nanofibers?TiO2/N-C NFs?were designed and successfully prepared by electrospinning using inexpensive and clean urea as nitrogen source and pore former.The introduction of nitrogen atoms in the carbon layer not only improves the electrical conductivity of the material,but also increases the sodium storage capacity of the material to some extent.Furthermore,the material's rate performance and reversible capacity are significantly improved.The large specific surface area not only provides more Na⁺embedded active sites,but also increases the contact area with the electrolyte,shortens the Na⁺/e^-transmission distance,and significantly improve the electronic conductivity of the material.Thanks to the large specific surface area and the introduction of nitrogen atoms,TiO₂/N-C NFs exhibit a high reversible capacity(0.05 A g^-1,265.8 mAh g^-1),outstanding rate performance and excellent cycle performance(118.1 mAh g^-1 after 1000 cycles under5 A g^-1).