Study On Preparation And Electrochemical Performance Of Bismuth-based Anode Materials

Lithium metal resources are extremely scarce and non-uniformly distributed in the earth’s crust,resulting in high cost of Li-ion power batteries,which limits their wide application in energy storage^[1-2].Potassium ion batteries（PIBs）,with lower reduction potential and abundant potassium in the earth’s crust,are considered by researchers to be the most promising and alternative to lithium ion batteries（Li Bs）as a new type of energy storage devices^[3].Bismuth-based materials,as an alloy-like material.Due to the presence of high level of theoretical specific capacity,it can be used as the superior anode material for the potassium ion battery preparation^[4].However,such compounds suffer from relatively low electrical conductivity,large volume changes and particle aggregation,which can cause them to not perform as expected in batteries.In order to further improve the performance of bismuth-based alloy-like materials in potassium ion batteries,they are Bi₂S₃,Bi O₄,and Bi Te@C as bismuth-based materials and investigates their energy storage performance and potassium storage mechanism in potassium ion batteries,using a series of physical and chemical tests to investigate them,with the following strategies.（1）A sea urchin-like Bi₂S₃ material was prepared as the anode of potassium ion battery by one-step solvothermal method.This sea urchin-like structure of bismuth sulfide has two obvious characteristics:1.the large space inside the sea urchin-like structure can cope with the volume change of the material during the electrochemical process;2.the large aspect ratio of the primary structure nanorods not only increases the electrolyte contact area,but also shorts the diffusion distance of potassium ions.Thanks to the above structural advantages,the material has excellent galvanic characteristics and can retain 84.6%of the original discharge specific capacity after 500 cycles at a current density of 50 m A/g.Ex-situ XRD and non-in-situ TEM tests reveal the electrochemical reaction mechanism;GITT test at room temperature tells the reason for the excellent potassium storage performance from the perspective of ion diffusion.（2）By one-step solvothermal method,the uniformly distributed and elongated needle and rod shape Bi PO₄ is prepared,and the ion and electronic transmission can be effectively authorized by controlling the particle size nanosized;the surface carbon layer can well solve the problem of volume expansion.The Bi PO₄ material was found to be well crystallized by its XRD test.With a small current density of 50 m A/g,the discharge capacity of the material can reach a high level of 260 m Ah/g,and then 300 charge/discharge cycles are performed,and the capacity decay rate is only 0.059%per cycle.By conducting non-in situ XRD test,the reaction mechanism is clearly explained;by conducting GITT test and pseudo capacitance test at room temperature,the superiority of its potassium storage performance is told from the ion diffusion perspective and from the pseudo capacitance contribution perspective.（3）A carbon wrapped nanofiber Bi Te composite（Bi Te@C）with a self-supporting structure was carefully designed by electrostatic filament spinning technique.Due to the encapsulation of Bi Te nanoparticles in C nanofibers with multi-hole structure,the carbon cladding and nanostructure design can not only enhance the material electric conductivity,but also solve the problem of larger volume expansion and particle aggregation to improve the potassium storage performance;moreover,this self-supporting structure of electrode material is flexible and does not require binder,conductive agent and collector,which reduces the proportion of inactive components and improves the overall specific capacity of the battery capacity.When the performance of charge/discharge cycle is tested with high current density（500 m A/g）,the discharge specific capacity can reach 385 m Ah/g,and after 800charge/discharge cycles,the discharge specific capacity can still be maintained at 211 m Ah/g.