Synthesis And Properties Of 2D Bismuth Element Nanosheet

Bismuth is located in the periodic table of the V group?Pnictogens?,which belongs to late transition metal,and the structure is layered similar to the same system of arsenic and antimony.In recent years,bismuth has attracted much attention due to its ultra-high theoretical volumetric capacity,but the volume has changed greatly during the charging/discharging process,resulting in irreversible loss of capacity.Based on the property of layered structure,the few-layer bismuthene was prepared by liquid phase stripping method.It was combined with graphene to be used as a anode electrode material for sodium-ion battery,which effectively alleviated the volume expansion and showed excellent electrochemical performance.In-situ technology and simulation calculations reveal the mechanism of sodium storage,which provides new ideas and strategies for future high-performance battery systems.The main content of this dissertation could be divided as following:?1?FLB was successfully prepared by a facile mechanical stripping method with a thickness of about 3-5 nm and a lateral dimension of 300-1500 nm.The effects of experimental factors such as stripping solvent,reaction time and reducing agent concentration on the morphology of FLB were systematically investigated.In addition,the self-supporting flexible FLB-G composite films with different loadings were prepared by simple vacuum filtration.The composite structure encapsulates the FLB between the graphene sheets,effectively preventing oxidation of the FLB.In addition,the composite membrane exhibits a three-dimensional network porous structure,which not only facilitates the rapid diffusion of ions,but also further alleviates the volume expansion phenomenon during electrode phase transformation,providing a new method for the design of sodium-ion battery material.?2?The prepared composite film was directly applied to the SIB anode electrode without adding conductive agent or binder.The composite electrode material exhibits excellent electrochemical performance with a good reversible redox peak and a suitable voltage charging and discharging platform.The rate performance and cycle stability of the electrode material are excellent.Even at high current density,the capacity of the electrode has not declined after 1000cycles,which is mainly due to the synergistic effect of the two-dimensional structure of FLB and the three-dimensional network structure graphene.Further,by adjusting the mass loading of the FLB-G electrode,the thickness of the composite film can be controlled,and the area capacity linearly increases with the increase of the mass loading,and the area capacity can be up to 12.1 mA h cm^-2,and the Coulomb efficiency of the electrodes after 50 cycles of different loading are about 100%,which provides a reliable choice for high-performance electrode scale control.?3?In-situ TEM,XRD datum and simulation calculations show that sodium ions are first embedded along the x-axis,and two phase inversions are formed into NaBi which is then converted into Na₃Bi during charging and discharging of the battery,The intercalation reaction contributes less capacity and does not change the structure;while the alloying reaction contributes to the main capacity,but severe volume expansion occurs,resulting in capacity decay.The volume expansion of Bi during the sodiation process is anisotropic:the expansion in the x/y plane is small,and the main expansion is as high as 142%in the z-axis direction.This reveals the charge storage mechanism of the alloy-based anode material,which provides a theoretical basis for the design of the electrode in the future.?4?FLB-G was converted into a composite electrode of Na-Bi alloy and graphene by galvanostatic cycling.The systematic electrochemical test shows that the Na-Bi alloy composite film electrode has excellent high current cycle stability,and the contours of the galvanostatic current charge and discharge curves are basically similar before and after cycling,and the potential of Na⁺deposition/extraction is the same.There is no significant polarization,indicating that the composite structure effectively reduces the local current density and alleviates the generation of sodium dendrites.Compared with the pure copper foil electrode,the Coulombic efficiency performance of FLB-G electorde is good.After 200 cycles,the Coulombic efficiency is stable at about 99.8%.The related electrochemical performance tests show that the Na-Bi alloy composite membrane electrode has low polarization potential,excellent Coulombic efficiency and good cycle stability,indicating that the sodium affinity and microstructure of the electrode material have great performance on the sodium anode batteries.At the same time,it shows that alloy graphene composite nanomaterials have potential applications in the field of sodium-ion battery anode.