Synthesis And Characterization Of Bismuth Nanomaterials As Lithium/Sodium Ion Battery Anode Material

Bismuth,when used as anode material,has gravimetric capacity of 386 mAhg-1,which is slightly higher than graphite(372 mAhg-1),but it reveals a fairly high volumetric capacity,about 3765 mAhcm-3 and possesses moderate operating voltage.Furthermore,its unique layered crystal structure is beneficial to Li+/Na+ insertion/extraction during process of electrochemical reaction,making bismuth available as a promising anode material for lithium/sodium ion battery.However,the weak electric conductivity and the large volume change of Bi materials during Li+/Na+insertion/extraction lead to a loss of electric contact and eventually rapid capacity fading,which severely impede its application.Nowadays,carbon-coating,nanocrystallization and structural design are effective methods for alleviating the volume changes and improving electrochemical performance.Firstly,Bi/GA composite was synthesized by combining with hydrothermal method and carbonation.First,flower-like Bi2S3 is obtained by hydrothermal method,and then the Bi2S3 and the graphene are ex-situ compounded to obtain the Bi2S3/GA composite material.Finally,the obtained composite material is carbonized at high temperature to obtain the Bi/GA composite.The results show that flower-like Bi2S3 is composed of nanowires with a diameter of about 10 nm,and each petal is uniformly coated with graphene after compounding.Because of confinement in the graphene shell,the microstructure of composite does not change after carbonization,but Bi2S3 is reduced to elemental Bi.At the same time,the evaporation of sulfur will generate voids to alleviate the impact of volume expansion,which are beneficial to enhancing the cycle stability and rate performance of the Bi/GA composite.In addition,we studied the commercial bismuth citrate into Bi/C composites by carbonization at different temperature.It is found that the Bi/C composite consist of Bi nanoparticles with diameter less than 50 nm and carbon-coating,and the Bi/C composite obtained at 700℃ shows that the carbon has graphene-like morphology.Electrochemical tests show that the discharge capacity of Bi/C composites at 600℃ reached 607 mAhg-1 after 150 cycles at a current density of 100 mAg-1 as an anode material for lithium ion battery.Finally,a novel structure was designed.Flexible and freestanding Bi/CNFs nanocomposites were prepared by electrospinning.Membranes consisting of CNF network structures bonded tightly with active Bi cluster materials,resulting in excellent mechanical protection and a fast charge transport path,which are difficult to achieve simultaneously.the discharge capacity of Bi/CNFs-1 reached 483 mAhg-1 after 200 cycles at a current density of 100 mAg-1 as an anode material for lithium ion battery.For use as a sodium ion battery,the Bi/CNFs-1 also shows an outstanding cycling performance(186 mAhg-1 at 50 mAg-1 after 100 cycles).This work offers a simple,low energy and eco-friendly method for fabricating free-standing and binder-free composite electrodes.