Syntheses And Electrochemical Properties Of Bismuth And Bismuth Oxide-based Materials For Lithium And Sodium Batteries

With the increasing severity energy problems,the rapid development of electric vehicles and mobile electronic products,people pay more attetion to new rechargeable batteries due to thier clean,high efficiency and energy density.To study the high energy density,volume energy density,high safety,flexible and low cost of battery anode materials are the key issue of the development and application for LIBs and SIBs.Lots of newly high volume density nano-materials such as Bi,Bi2O3,CuBi2O4 and CuO have the characteristics of safety and stability,low cost and easy synthesis,which are expected to develop the next generation LIBs and SIBs anode materials.Our study mainly focused to enhance the electrochemical performance of the above anode materials by improving the electrical conductivity,optimizing structure and nanocrystallization.(1)The Bi/C nanofibers have been prepared by a single-nozzle electrospun method with skillfully chosen Bi source and a subsequent carbothermal reduction process.The structural and morphological characterizations of the Bi/C nano fibers reveal that abundant Bi nanoparticles with a diameter of about 20 nm homogeneously dispersed and imbedded 1-D in carbon nanofibers.Electrochemical measurements indicate that the Bi/C nanofiber anodes could deliver a long cycle life for Li-ion batteries and preferable rate performance for Na-ion batteries.The superior electrochemical performances of the Bi/C nanofiber anodes are attributed to the 1-D carbon nanofibers structure and uniform distribution of Bi nanoparticles imbedded in carbon matrix.The unique structure provides a favourable electron carrier and buffering matrix for effective release of mechanical stress caused by volume change and prevents the aggregation of Bi nanoparticles.(2)The flexible binder-free film composed of bismuth oxide nanoparticles embedded in carbon nanofibers(Bi2O3/C)have been prepared by a feasible electrospinning and firstly used as a sodium ion battery(SIB)anode.As a binder-free and flexible anode for SIBs,Bi2O3/C delivers a high reversible capacity of 430 mA h g-1 after 200 cycles at a current density of 100 mA g"1 and an exceptional rate capability of 230 mA h g-1 at 3200 mA g-1.It has a stable capacity of 252 mA h g-1 after 50 cycles at 400 mA g-1 for Na-ion full cell device.The high capacity,good cyclability and rate capability are attributed to synergistic effects of the uniform distribution of ultra-small Bi2O3 nanoparticles(?10 nm)in carbon nanofibers and the conducting framework of 3-D interconnected carbon nanofibers,which can effectively alleviate the volume expansion during sodiation/desodiation process and maintain the high electrical conductivity throughout the electrode.This self-standing flexible Bi2O3/C nanocomposite electrode may hold great promise for high-performance SIBs.(3)Hierarchical CuBi2O4 microspheres have been prepared through a facile and eco-friendly hydrothermal route,and applied as anode materials for LIBs.The hierarchical CuBi2O4 microspheres of diameter about 2.0-4.0 ?m are assembled by crystalline tetragonal nanoparticles with a size of 50-60 nm.Electrochemical performance of the hierarchical CuBi2O4 microspheres shows strong temperature-dependence that higher temperature evidently enhances the electrochemical performance.At an elevated temperature of 70 ?,a reversible capacity of 525.1 mA h g-1 has been achieved after 500 cycles at a current density of 100 mA g-1.Even after being cycled at a high current density of 6.4 A g-1 the hierarchical CuBi2O4 microspheres are still able to deliver a capability of 585 mA h g-1 when the current density is set back to 100 mA g-1.The superior high-temperature electrochemical performance of the hierarchical CuBi2O4 microspheres is ascribed to their hierarchical structure and outstanding thermostability.(4)Hollow porous CuO/C composite microcubes have been prepared by controlled pyrolysis of[Cu3(btc)2]n(btc = benzene-1,3,5-tricarboxylate)metal-organic frameworks(MOFs).SEM and TEM images indicate that the as-prepared CuO/C microcubes possess uniform appearance with hollow porous structures.Electrochemical measurements show that the hollow porous CuO/C composite microcubes deliver a highly reversible capacity of 510.5 mA h g-1 after 200 cycles at a current density of 100 mA g-1.Due to its hollow porous structure and the enhanced conductivity of residual carbon,the rate performance delivers excellent reversible capacity of 232.78 mA h g-1 at a high current rate of 3.2 A g-1.The recycled morphology could remain the original structure,further indicating that the microcubes are resistant to collapse and more suitable for lithium-ion batteries storage materials.