Dimensional Manipulation And Mechanism Study To High-Performance Bismuth-based Anode For Sodium/Potassium-ion Batteries

In recent years,bismuth-based materials have attracted widespread attention when used as anode materials for sodium and potassium ion batteries,owing to their lower reaction potential and higher theoretical specific capacity and energy density.However,these materials face the challenge of huge volumetric variation during the charge and discharge process,leading to the pulverization of the pulverization of the electrode materials and detachment from the current collector during the repeated cycles,which may result in fast capacity attenuation.To solve these problems,this dissertation adopts dimensional structure design strategies combining with carbon material composite,electrolyte modification and other strategies to alleviate the volumetric variation and improve the structural stability of the materials.With rational structure design,the excellent rate performance and cycle life of bismuth-based materials in sodium/potassium ion batteries are realized.The reaction mechanism in the process of sodium/potassium storage are systematically investigated and revealed through a variety of characterization strategies.In chapter 1,the general situation of sodium/potassium ion batteries and the research progress of bismuth-based anode materials are systematically reviewed.In chapter 2,an overall introduction to the drugs,instruments,equipments and characterization methods used in the experiments of this dissertation is presented.In chapter 3,via the high-temperature pyrolysis and self-assembly of triphenylbismuth,the bismuth nanospheres embeded in 3D graphene framework(Bi@3DGFs)is prepared.Owing to the fast ion transmission and the excellent electrical conductivity brought by 3D porous graphene frameworks(3DGFs),and the shorter diffusion path of the nano-sized bismuth,the Bi@3DGFs exhibits superior rate capability and cycling performance for sodium and potassium ion storage.In chapter 4,by designing a heterostructure of one-dimensional(1D)ultrafine bismuth nanowires and two-dimensional(2D)graphene nanosheets,a flexible freestanding film is obtained.Owing to the ultra-short radial size of 1D nanowires and the conductivity of 2D graphene nanosheets and the buffering effect on volume expansion,the freestanding anode material is used in NIBs and delivers good electrochemical performance.In chapter 5,three-dimensional continuous porous bismuth(3DPBi)is prepared by liquid-phase reduction reaction.Its unique nanostructure combines 3D continuous Bi nanoligaments and continuous nanoporous network,providing unblocked electronic circuit and short ion diffusion path and the accommodation for huge volumetric changes.The 3DPBi anode exhibits unprecedented electrochemical performance in terms of sodium storage.It delivers a capacity retention of 95.6%at 60 A g-1 with respect to 1 A g-1 and maintains a capacity of 378 mA h g-1 after cycling at 10 A g-1 for 3000 cycles.Through in-situ and ex-situ TEM observations,the self-healing of volume changes was revealed.In addition,the Na3V2(PO4)3|3DPBi full cell has high energy density(116 W h kg-1)and stable cycling performance(273 mA h g-1 after 150 cycles),proving its prospect in practical applications.In chapter 6,we systematically investigate the morphological evolution of different dimensions of Bi(from zero to three dimensions)during the alloying reaction in potassium ion batteries.Among them,2D-Bi evolves into continuous porous bismuth nanoligaments that maintains the original nanosheet shape after cycling,which shorten the ion diffusion path and buffer volume expansion during the cycle.In-depth XPS analysis shows that the SEI film derived from ether-based electrolyte contains polyether,fluorine-containing organic compound and KF,which is thin and tough.Owing to the stable derivative structure and tough SEI film,2D-Bi exhibits excellent long-cycle performance and rate performance in potassium ion batteries.In-situ XRD further improved the stepwise potassiumization/depotassization reaction mechanism:Bi?KBi2?K3Bi2?h-K3Bi/c-K3Bi.Density functional theory(DFT)-based calculations and ab initio molecular dynamics simulations revealed the rapid reaction kinetics between Bi and K from the atomic scale.In addition,the full cell(2D-Bi//PB)paired with Prussian blue exhibits stable cycling performance and excellent rate performance.The full cell provides a stable voltage output of 2.85 V and high energy density(174 W h kg-1 and 475 W kg-1),proving the application prospects of 2D-Bi for potassium ion storage.In chapter 7,we summarize the works in this dissertation,point out the innovations and shortcomings of the work,and look forward to the work content of the next stage.In addition,in the appendix part of the dissertation,we introduce the research on the material structure design and modification of the transition metal cobalt chalcogenide as the anode material of the sodium ion batteries.