Study On The Preparation And Electrochemical Performance Of Tin-based Hybrid Carbon Nanofibers

Conventional carbon material electrodes are increasingly unable to meet people's needs due to their small storage capacity.Inorganic hybrid carbon nanofibers possess both inorganic and carbon nanofiber properties and have received extensive attention from researchers.Among them,metallic Sn and SnO2 both have the advantages of high electrical conductivity,high theoretical capacitance,stable chemical properties,and good acid and alkali resistance.In this thesis,Sn-containing compound is added into the spinning solution,and the fluffy Sn-based hybrid carbon nanofibers mats with the diameter of 40 cm are prepared by airspinning and high temperature calcination in inert atmosphere.The nanofibers possess an inseparable two-layer structure.The upper layer is the Sn-based nanostructure,and the lower layer is the hybrid carbon nanofibers containing a small amount of Sn-based nanoparticles.The upper nanostructures are sequentially obtained with nanoparticle,nanowire and nanocolumn as the holding time is prolonged.Since no metal catalyst is added or a reducing atmosphere is introduced during the entire calcination process,the nanowires are obtained by autocatalytic growth and follow the VLS growth mechanism.The nanofibers possess excellent capacitance performance as an electrode material.The specific capacitance of the sample maintained at 1300? for 3 h can reach 403.6 F g-1 at a current density of 0.5 A g-1;its specific capacitance still retains 162.5 F g-1 even at a high current density of 10 A g"1;its specific capacitance reaches 358.9 F g-1 at a scan rate of 10 mV s-1;its charge transfer resistance is only 1.3 ? and its capacitance retention is 92.5%after 3000 cycles at the current density of 1 A g-1.The upper nanostructures of Sn-based hybrid carbon nanofibers are formed by the overflow of Sn source.Although there is a synergistic effect between the Sn-based nanostructures and the hybrid carbon nanofibers,the overflow of Sn source inevitably causes damage to the structure of the bottom hybrid carbon nanofibers.The addition of Si-containing compound can effectively solve problems of overflow of Sn-containing compound and agglomeration of Sn-containing compound inside the nanofiber.There is no chemical reaction between the Sn-containing compound and the Si-containing compound,and thus,the Si source only serves as a physical isolation.Compared with Sn-based hybrid carbon nanofibers,the discharge capacity and cycle stability of Sn/Si based hybrid carbon nanofibers are improved.The specific capacitance of the sample maintained at 1400 ? for 3 h can reach 419 F g-1 at a current density of 0.5 A g-1;its specific capacitance can still retain 198.6 F g-1 even at a high current density of 10 A g-1 and its capacitance retention can reach 95.1%after 3000 cycles at the current density of 1 A g-1.Sn-based and Sn/Si based hybrid carbon nanofibers both show excellent capacitance performance which may achieve large-scale application in the electrode materials of capacitor,or will be further extended to the electrode materials of lithium ion batteries,lithium-sulfur batteries and other energy storage devices.