Preparation Of Carbon/Carbon Composite Nanofiber Materials And Its Sodium Storage Performance

Lithium ion batteries have been successfully used in advanced electronic devices and electric vehicles,thanks to their high energy density,power density and long-cycle stability.Nevertheless,the uneven distribution in the earth,the extremely limited lithium reserves and lithium’s rising cost make the lithium ion batteries not suitable for large-scale energy storage.Sodium and lithium have similar physical and chemical properties.Due to the low cost and abundant sodium resources around the world,sodium ion batteries grow rapidly as a new star of large-scale energy storage.Considering the advantages of low cost,stable chemical properties,and environmentally friendliness,carbon materials have become the most promising anode materials for sodium ion batteries.Carbon nanofibers with high long-aspect ratio,excellent mechanical strength and flexible and tunable structure,were selected as the basic object of research.And nanocarbon additives were introduced in carbon nanofibers to study the interaction between different nanocarbon additives and carbon nanofibers.Besides,after introducing nitrogen,the effect of different nanocarbon additives on carbon nanofibers was investigated.The main research contents are as follows:（1）The carbon nanofibers skeleton was prepared from polyvinylpyrrolidone as carbon source,and carbon nanotubes and graphene were used as conductive additives to prepare cross-linked carbon/carbon composite nanofibers.A three-dimensional conductive network constructed from the cross-linking nanofibers network was conducive to the rapid transmission of electrons.The introduction of graphene promoted the evolution of functional groups on the surface of the material.The abundant surface functional groups effectively improved the sodium storage capacity and enhanced the electronic conductivity of the material.At a current density of 0.05A g^-1,the reversible capacity of the G/CNFs electrodes achieved 254 m Ah g^-1 after300 cycles.The capacity of the G/CNFs electrodes remained at 200 m Ah g^-1 at 2 A g^-1after 600 cycles.Quantitative kinetic analysis found that the sodium storage behavior of the material（G/CNFs）was dominated by the surface Na⁺adsorption.（2）Melamine was used as nitrogen sources to prepare nitrogen doped carbon nanofibers,and after introducing graphene,it showed excellent sodium storage capacity.The presence of graphene promoted the evolution of nitrogen-containing functional groups on the surface,created massive pore structures on surface and expanded the layer spacing.It played an important role in enriching the active sites,increasing the interlayer sodium storage capacity,and significantly promoting the electrochemical properties.At 0.05 A g^-1,the initial charge capacity of N-G/CNFs electrode reached 310 m Ah g^-1.After 200 cycles at 0.05 A g^-1,a capacity of 295 m Ah g^-1 can be achieved in N-G/CNFs electrode achieved,which was much higher than that of N-CNFs(193 m Ah g^-1).At the same scan rate,the pseudo-capacitance contribution of N-CNFs electrode materials was higher than that of N-G/CNFs,indicating that the intercalation reaction in the N-G/CNFs electrode had an important contribution to increasing sodium storage capacity.