Morphological Construction And Lithium/Sodium Storage Properties Of Tin-Carbon Nanofibers

Due to its high theoretical capacity,abundant natural resources,suitable voltage platform,and dual applicability to lithium/sodium ion batteries,the research and application of tin based negative electrode materials have received great attention.However,due to poor conductivity and significant volume expansion during cycling,the commercial application of tin based materials is severely limited.In order to improve these defects,this study utilized electrospinning technology to prepare a series of tin based carbon nanofiber composites through morphology construction,composite modification,and other methods.The structure,morphology,and lithium/sodium storage properties of these composites were thoroughly studied through certain characterization methods and electrochemical analysis methods.The main content is as follows:（1）Optimization preparation and lithium storage performance research of one-dimensional tin carbon nanofiber composite materials.Preparation of tin polymer nanofiber precursors using electrospinning technology,optimization of carbonization temperature,and preparation of tin carbon nanofibers with optimal performance（Sn-Sn O_x@CNF）Composite materials.A detailed comparison was made on the differences in microstructure,composition,and lithium storage performance of composite materials under different carbonization temperatures.It was found that the nitrogen content of the composite materials obtained by carbonization at high temperatures of 700℃significantly decreased,and large particles of Sn gathered on carbon nanofibers.The composite material obtained at a lower carbonization temperature of 500℃has a low degree of graphitization of carbon fibers and contains a large number of defects,which is not conducive to the insertion and removal of lithium ions,and has poor lithium storage performance.And carbonization at 600℃results in Sn-Sn O_x@CNF-600 Composite materials have high graphitization degree and nitrogen content in their carbon fibers,and nanoscale tin and its oxides are uniformly distributed in the carbon fibers,exhibiting good lithium storage performance.After 100 cycles at a current density of 1.0 A g^-1,their specific capacity remains at 596.1 m Ah g^-1.（2）Construction of multi-channel hollow tin carbon nanofiber composite material and its lithium/sodium storage performance research.Using polymethyl methacrylate（PMMA）as a template for spinning construction,tin carbon nanofibers with multi-channel hollow carbon nanofiber structure were prepared（Sn-Sn O_x@MCNF）Composite materials.Research shows,Sn-Sn O_x@MCNF Composite materials have excellent lithium/sodium storage properties.As a negative electrode material for lithium-ion batteries,after 600 cycles at a current density of 1.0A g^-1,its specific capacity remains at 669.2 m Ah g^-1,and even at a high current density of 4.0A g^-1,its specific capacity is still as high as 525.1 m Ah g^-1.As a negative electrode material for sodium ion batteries,its specific capacity can maintain 356.0 m Ah g^-1 after 100 cycles at a current density of 0.1 A g^-1.This well compatible lithium/sodium storage performance is mainly attributed to the uniform distribution of nano Sn and Sn O_x in multi-channel hollow carbon nanofibers,which is not only conducive to the rapid transport of ions and electrons and the reversibility of electrode reaction,but also can effectively buffer the volume expansion during the cycle and maintain the stability of the SEI film on the electrode surface,thereby improving the structural stability and cycle life of the electrode materials..（3）Preparation and lithium/sodium storage properties of Cu-Sn bimetallic modified multi-channel carbon nanofiber composites.In order to further improve the electrochemical performance of tin carbon composite materials,Cu Sn alloy nanospheres were prepared by doping Cu element and dispersed in multi-channel carbon nanofibers with low tin content（Cu Sn-Sn O_x@MCNF）Composite materials.As a negative electrode material for lithium-ion batteries,it still maintains a high specific capacity of 785.1 m Ah g^-1 after 600 cycles at a current density of 1.0 A g^-1.When used as a negative electrode material for sodium ion batteries,after1000 cycles at a current density of 1.0 A g^-1,it still maintains a high specific capacity of 340.1m Ah g^-1,and even at a high current density of 4.0 A g^-1,it still maintains a reversible capacity of 202.5 m Ah g^-1.This excellent lithium/sodium storage performance can be attributed to the formation of Cu Sn alloy nanospheres,which reduces the tin content in multi-channel hollow carbon nanofibers and further improves their cycling stability;Secondly,the catalytic graphitization effect of Cu on carbon materials during the carbonization process,as well as the more stable structure and conductivity of Cu Sn alloy nanospheres compared to Sn,enhance the ion and electron transport ability of the composite material,thereby improving the cycling and rate performance of the electrode material.