Synthesis And Electrochemical Characterization Of Bismuth/Antimony Sulfide As Anode For Lithium/Sodium Ion Batteries

Bismuth and antimony-based materials especially Bismuth/Antimony sulfide possess much higher theoretical capacity than commercial graphite,relatively low operating voltage,and special interlayer structure which facilitates the intercalation-extraction of Li+/Na+,making it a promising anode candidate for Lithium and Sodium ion batteries with broad prospects.However,similar to most electrode materials,low electric conductivity and large volume expansion caused by the interlaminar deintercalation of Li/Na ions leads to great loss of electric contact which severely hinders the application in practice.Currently,nanocrystallization and structural design and conductive buffer phase construction are effecitive solutions to simultaneously improve conductivity and electrochemical performance.In this study,Bi2S3/FC composites were prepared by hydrothermal method and carbonization.Firstly,one-dimensional rod-shaped Bi2S3 was prepared by hydrothermal treatment,Secondly,PVDF was used as the fluorocarbon source for the ex-situ liquid phase impregnation and glucose was used as the undoped carbon source for comparison,followed by carbonization under the same conditions.It was found that the Bi2S3 nanorods are uniformly coated by an amorphous fluorocarbon layer with 5nm in thickness.The presence of the fluorocarbon layer greatly improved the electric conductivity and the first coulombic efficiency of Bi2S3.The reversible capacity of Bi2S3/FC-1 reached 584.3mAh/g after 100 cycles at the current density of 0.2A/g as anode for Li-ion battery,and the morphology was well preserved during the process of charge and discharge.In addition,we also studied the Sb2S3/FC core-shell nanowires with different fluorocarbon coating thickness.The results showed that the nano wires have a diameter of 90-120 nm and a length of tens of micrometers.As the amount of PVDF increases,the thickness of the fluorocarbon layer increases with 3.7,7.9 and 11.7 nm.When used as anode for Li-ion battery,Sb2S3/FC-1 delivered a discharge capacity of 917.4mAh/g at 0.1A/g,even at 2A/g,a reversible capacity of 422.9mAh/g still can be reached.For use as Sodium-ion battery anode,Sb2S3/FC-2 and Sb2S3/FC-3 showed much stable capacity at high rate,while capacity retention of Sb2S3/FC-1 is the highest(86.1%)when the current density returns to 0.1 A/g.Finally,the Bi-Sb-S ternary sulfide nanostructures with different Bi/Sb ratios were prepared by hydrothermal method,a thin SiO2 shell was designed to suppress volume expansion and make full use of synergistic effect between Sb2S3 and Bi2S3 phase.It was found that the SiO2 layer facilitates the formation of a stable and thin SEI film,resulting in excellent mechanical protection and achieves a higher coulombic efficiency for the first cycle.The reversible capacity of SiO2/Bi-Sb-S-1 reached 587.8mAh/g after 100 cycles at a current density of 0.2A/g and 511mAh/g even at higher rate of 2A/g as an anode for Sodium-ion battery.When tested as anode for Li-ion battery,SiO2/Bi-Sb-S-1 also shows good cycling performance(740 mAh/g after 100 cycles at 0.1 A/g)with a capacity loss of only 13%.