Design And Preparation Of High-Performance Titanium Dioxide And Phosphorus Based Anode Materials For Sodium/Potassium-ion Batteries

In recent years,energy storage technology is one of the core technologies urgently needed to realize the popularization and application of renewable energy generation such as solar energy,wind energy,and the construction of smart grid.The development trend of clean energy requires that the future development direction of energy storage technology must be:low-cost,long-life,high-efficiency energy storage batteries.The development of sodium/potassium batteries is critical to the development of large-scale energy storage technologies.The electrochemical performance of the electrode material is one of the keys to determine the battery performance.The development of anode materials is critical to the development of sodium/potassium batteries.This thesis focus on the preparation,performance optimization and energy storage mechanism of high-performance anode materials for sodium ion batteries and potassium ion batteries.This thesis mainly focus on TiO₂ and red phosphorus two types of anode materials.When TiO₂ is used as anode material for sodium ion batteries,it has received extensive attention due to its low sodium-embedded potential and good structural stability.As a kind of alloy-typed anode material,red phosphorus shows great potential in sodium/potassium ion batteries due to its high theoretical specific capacity.However,both of these materials have the disadvantages of low electronic conductivity.Therefore,this paper improves the electronic conductivity and mitigates the volume effect through one-dimensional structural design and carbon material incorporation.In chapter 1,we described the research background of sodium/potassium-ion batteries and the development status of TiO₂ and phosphorus-based anodes.In chapter 2,we introduced the experimental instruments and reagents used in this paper,as well as the testing methods of the electrochemical performance.In chapter 3,we used the electrospinning and the subsequent Ar/NH₃ treatment process to successfully fabricate the nitrogen-doped ordered mesoporous anatase TiO₂ nanofibers anode with superior sodium storage performance.A high reversible capacity of 110.07 mAh g-1 at a current density of 10 C could be achieved.The excellent electrochemical performance is attributed to the presence of the mesoporous structure and Ti3+/oxygen vacancies,which can shorten the ion diffusion path and improve the electronic conductivity of TiO₂ material.In chapter 4,the one-dimensional multi-channel porous TiO₂ nanofibers with rich oxygen vacancies have been fabricated via electrospinning and subsequent vacuum treatment process.Excellent sodium storage performance could be obtained:at the high current density of 20 C,a high reversible capacity of 93 mAh g-1 could be maintained after 4500 cycles.Excellent long cycling stability and rate performance could be ascribed to the rich oxygen vacancies and the multi-channel fibrous structure.In chapter 5,the multichannel porous TiO₂ nanofibers with well-dispersed Cu nanodots and Cu2+-doping derived oxygen vacancies have been fabricated via electrospinning.The anode material exhibits excellent rate performance and long cycle stability:a high reversible capacity of 120 mAh g-1 at 20 C could be achieved.Cu2+ doping can improve the electronic conductivity of TiO₂ matrix,reduce the transport energy barrier of Na+,thereby promoting the migration of ions and electrons.In chapter 6,this chapter designed the red phosphorus embedded in the porous carbon matrix with graphene and MOF-5 derived sandwiched structure via the evaporation-deposition method.The unique porous structure of the carbon matrix can effectively improve the electronic conductivity and alleviate the volume change of red phosphorus during change/discharge process,demonstrating excellent cycling performance and rate performance:at a large current density of 10 A g-1,the reversible capacity could be achieved at 502 mAh g-1.In chapter 7,this chapter successfully prepared the red P embedded into the self-supported nitrogen-doped hollow porous carbon nanofibers via the evaporation-deposition method.The composite exhibits excellent potassium storage performance:at a current density of 2 A g-1,there is still 465 mAh g-1 potassium storage capacity after 800 cycles.At the same time,the in-situ TEM,in-situ Raman and ex-situ XRD tests were carried out on the charge/discharge mechanism of the composite anode.In chapter 8,we pointed out the innovations and the areas that need to be improved and look forward to the future research work.