Preparation And Energy Storage Properties Of Sn-based Carbon Nanofiber Composites

The development and application of new functional fibers opened up a new research field of dyeing and finishing.With the continuous development of consumer lithium-ion batteries,dyeing and finishing technologies used in the preparation of energy storage functional fibers are now designed to meet the market demand.Accordingly,the Tin?Sn?-based carbon nanofiber?CNF?composites can achieve energy storage function when combined with the energy storage characteristics of Sn-based materials and the high conductivity of CNFs.According to the large volume change of Sn-based materials,the morphology and structure were designed by internal modification and external protection.Based on the analysis of the composition,structure and energy storage performance of Sn-based CNF composites prepared by different methods,the energy storage mechanisms were discussed.Chapter 1 includes a general introduction about the research background and working principle of lithium ion batteries?LIBs?.After making a generalized summarization for the Tin?Sn?based anode materials,a particular summary is provided on the research status of Sn-based materials of LIBs.In chapter 2,we demonstrate the fabrication of Sn nanoparticle-loaded porous carbon nanofibers?Sn-PCNFs?via the electrospinning and subsequent carbonization.This is shown to result in an even distribution of pores on the surface of the nanofibers,allowing the Sn-PCNFs to be used directly as an anode in lithium-ion batteries without the need to add non-active materials.With a discharge capacity of 774 mA h g^-1 achieved at a high current of 0.8 A g^-1 over 200 cycles,this material clearly has a large capacity.However,the specific capacity fades rapidly in the first 25 cycles,which would seem likely to be the result of severe pulverization caused by the dramatic volume change of large Sn-based particles.In chapter 3,from the point of using the spilt Sn-based particles view,we fabricated a rational design of Sn-Cu alloy/CNF composite?Sn-Cu-CNFs?anodes via one-step carbonization-alloying reactions to avoid the pulverization of the spilt Sn particles.The spilt Sn-Cu alloys consist of active Cu6Sn5 and inactive Cu3 Sn,and are controllable by optimization of the carbonization-alloying reaction temperature.These composite anodes exhibited a stable cyclability with a discharge capacity of 400 mA h g^-1 at a high current density of 1.0 A g^-1 after 1200 cycles,as well as an excellent rate capability,which could be attributed to the improved electrochemical properties of the Sn-Cu-CNFs provided by the buffering effect of Cu3 Sn.In chapter 4,a carbon-coated composite consisting of Sn,SnO₂,and CNFs?Sn–SnO₂–CNF@C?was successfully prepared via low-temperature hydrothermal treatment.The thickness of the carbon overlayer formed by using sucrose as the carbon source could be well controlled by adjusting the sucrose concentration.The Sn–SnO₂–CNF@C2 electrodes exhibited a high discharge capacity of 712.2 mA h g^-1 at a high current density of 0.8 A g^-1 after 200 cycles,as well as good cycling stability and excellent rate capability,which can be ascribed to the improved electrochemical properties of the Sn-based particles provided by the protective carbon coating.In chapter 5,the UV20-CNFs and UV20-Sn-CNFs bearing oxygen-containing functional groups and inhomogeneous nanopores were first fabricated using excimer UV radiation.When evaluated for their potential for use as an anodic material in rechargeable Li-ion batteries,the UV20-Sn-CNFs and UV20-CNFs demonstrated excellent cycling stability(UV20-Sn-CNFs: 733 mA h g^-1 at 0.8 A g^-1 after 200 cycles,UV20-CNFs: 300 mA h g^-1 at 2.0 A g^-1 after 1000 cycles).The improved electrochemical performance was attributed to the chemically bonded solid electrolyte interface?SEI?films on the CNF surface and inhomogeneous nanopores for Lithium ion storage and fast diffusion.The excimer UV radiation is a promising approach that may enable the commercial implementation of high capacity electrode materials for long cycle life Li-ion batteries.Finally,in chapter 6,an overview and the deficiency of the dissertation are summarized.Some prospects on the possible future research are presented.