Preparation And Sodium Storage Properties Of Transition Metal Compound/carbon Composite Nanofibers

Over Lithium-ion batteries have been widely studied and applied on a large scale because of their high energy density and power density.However,the reserves of lithium resources are limited and the distribution of lithium resources is uneven,which limits the sustainable development of lithium ion batteries.Sodium ion battery is a potential energy storage system instead of lithium ion battery due to its rich and uniform distribution of sodium resources.In recent years,transition metal oxygen(sulfur)compounds have attracted much attention because of their theoretical capacity,good safety and wide range of sources.However,they have problems such as poor electrical conductivity and poor structural stability.Composite and nano crystallization of transition metal oxygen(sulfur)compounds with carbon is expected to improve the above problems and obtain high-performance cathode materials for sodium ion batteries.In this paper,two kinds of transition metal oxide(sulfide)/carbon composite nanofibers were prepared by electrospinning.The structure-electrochemical properties of these nanofibers were studied.(1)Using phenolic resin/polyvinylpyrrolidone(PVP)as carbon precursor and copper nitrate as copper source,CuO/C composite nanofibers were prepared by electrospinning combined with curing and carbonization process.The effects of different carbonization temperatures on the microstructure and electrochemical properties of the composite nanofibers were investigated.The results show that at different carbonization temperatures,the fiber diameter of the composite nanofibers is about 400 nm,and the particles precipitated on the fiber surface are mainly CuO phase,and the particle size increases with the increase of carbonization temperature.With the increase of carbonization temperature,the specific surface area first decreases and then increases.With the increase of carbonization temperature,the maximum capacity of composite nanofibers was obtained at 600?,and the specific capacity reached363.8 m Ah g^-1when the current density was 0.05 A g^-1.With the increase of carbonization temperature,the ratio and cycling properties of the samples increased first and then decreased.The carbonization temperature of 800?is the best,and the capacity retention is 35.7%at 2 A g^-1 high current density,and 51.7%after 100 cycles at 0.01 A g^-1 current density.(2)Using phenolic resin/PVP as carbon precursor and iron acetylacetone as iron source,FeS/Fe₂O₃/C composite nanofibers were prepared by electrospinning combined with carbonization and vulcanization process.The effect of the amount of iron source on the microstructure and electrochemical properties of the composite nanofibers was investigated.The results show that the particle diameter on the fiber surface increases with the increase of the amount of iron source,and the particle size on the fiber surface is mainly composed of Fe₂O₃ and FeS.With the increase of iron source,the specific surface area of the composite nanofibers increased gradually,and the maximum specific surface area was 100.7 m₂ g^-1 for the sample with the mass ratio of phenolic resin/iron acetylacetone of 1?4.With the increase of the phenolic resin/acetylacetone iron mass ratio,the ratio of the composite nanofibers and their cycling properties were improved.When the mass ratio of phenolic resin/iron acetylacetone was 1?4,the composite nanofibers had an initial reversible capacity of 350.0 m Ah g^-1 at the current density of0.05 A g^-1,and A capacity retention rate of 76.3%at A current density of 2 A g^-1.After100 cycles,the capacity retention rate was 97.2%.