Synthesis And Electrochemical Performance Of Tin-based Anode Materials Loaded On Carbon Nanofiber

With the wide application of lithium-ion battery,the demand for capacity and cycling performance of lithium-ion batteries was also increasing,the anode material of the commercial lithium-ion battery was graphite,with theoretical capacity of only 372 m A g-1,which is difficult to meet the needs of the development nowdays.The tin-based anode material has a high specific capacity,abundant reserves and low cost,etc.,which is great concern and is expected to replace graphite as the anode material for the next generation lithium-ion battery.However,the tin-based anode material display large volume change during charge-discharge process,this will cause the electrode material agglomerated and pulverized,even poor contact with the current collector or shedding,resulting in capacity decay rapidly and poor cycling performance.In order to overcome the volume expansion and other defects of tin-base anode materials,this paper attempts to use different raw materials,carbon nanofibers as the substrate,synthesis of carbon nanofiber-supported tin oxide composites,in order to suppress the volume expansion of tin-oxide,thus improving the cycling performance,and the composite material has good flexibility,dispense with current collector,which avoided the problem of poor contact between the electrode material and the current collector.The specific research contents are as follows:1.Based on CNF film,use SnCl₄·5H₂O,Na OH and glucose as raw materials to synthesis the carbon-coated carbon nanofiber/tin-based composite material（CNF/SnO₂@C）by two-step hydrothermal and carbonization processes.Analyzed the morphology and structure of the material by XRD,SEM,TEM and XPS,and the electrochemical properties of the materials were investigated by cyclic voltammetry,charge-discharge cycles and EIS test.The reseach shows that the synthesized of SnO₂ submicron particles with more uniform size after adding CNF film,about 2 μm.Compared with SnO₂@C sample,CNF/SnO₂@C sample shows better cycling performance and rate performance.2.Use Sn Cl2·2H₂O as tin source,synthesized the carbon-coated carbon nanofiber/tin-based composite material（CNF/Sn|SnO₂@C）.CNF provide a substrate for generation of Sn|SnO₂ particles and surface sponge carbon.In the charge-discharge processes,CNF and sponge carbon on the surface effectively suppress the Sn|SnO₂ particles volume expansion,and provide a fast channel for electronic transmission,increased the composite conductivity,thus CNF/Sn|SnO₂@C electrode shows good cycle performance and rate performance.After 50 cycles at the current density of 0.1A g-1,the capacity remain at 657.6 m A h g-1,the rate performance is 457 m Ah g-1 at 2A g-1.3.Use different alkaline sources,it was find that the carbon-coated carbon nanofiber/tin-based anode material（CNF/SnOx@C）synthesized by LiOH shows the most uniform size of SnOx particles and the best electrochemical properties.Under the current density of 0.1 A g-1 after 300 cycles,the capacity remain at 726.9 m A g h-1,the rate performance is 382.6 m Ah g-1 at 2A g-1,which was significantly higher than the composite materials synthesized by other alkaline sources.4.Carbon coated carbon nanofibers/tin-based composites（CNF@SnO₂@C）were synthesized by a simple one-step hydrothermal method.The CNF@SnO₂@C composite obtained by this method not only has the good flexibility and electrochemical stability of CNF film,but also maintained the high specific capacity of SnO₂.The capacity remained at 763.2 m A h g-1 after charging and discharging 200 times at the 0.1A g-1.When the current density increases to 2 A g-1,the capacity remain at 307.8 m Ah g-1.