Preparation And Electrochemical Properties Of CNT/Fe₃O₄ Nanocomposites Based On Polymer Nanotubes As A Carbon Source And Template

As an anode material for lithium ion batteries,Fe₃O₄ has raised wide attention because of its high theoretical value(924 mAh g^-1),eco-friendliness,low cost,and natural abundance.However,the low conductivity of electrons and ions hindered the development of such materials.At present,the construction of one-dimensional CNT@Fe₃O₄ nanocomposites with CNTs is an effective way to improve the reversible capacity of Fe₃O₄.In this paper,CNT@Fe₃O₄ and CNT@Fe₃O₄@C nanocomposites were constructed by using the sulfonated polymer nanotubes as the carbon source and template,which addressed the problems of severe aggregation,inferior electronic and ionic conductivity,and large volume variation of Fe₃O₄ nanoparticles,improved the mechanical stability of Fe₃O₄-based anode materials.Meanwhile,the morphologies and structures of the materials were characterized by a variety of analysis methods,the strong synergistic mechanism of Fe₃O₄ and carbon was discussed,and the effect of composite structure on the electrochemical performance of the electrode was also studied,which is a theoretical basis for the development and application of Fe₃O₄-based anode materials.Specific research contents are as follows:1.Porous CN T@Fe₃O₄ nanocomposites were fabricated by using the co-precipitation method and the subsequent thermal treatment: ferric nitrate was acted as an iron source and sulfonated polymer nanotubes as carbon source and template.Sulfonated polymer nanotubes pretreated with ammonia?25 %?,then porous CNT@Fe₃O₄ nanocomposites were successfully prepared by the co-precipitation method and calcination.Meanwhile,the effect of solvent and pH during the preparation of precursors on properties of composites was discussed.The results showed that the electrochemical properties of the composites were better under the weakly alkaline conditions,which exhibited a favorable specific capacity of 770.3 mAh g^-1 at 500 mA g^-1 after 300 cycles and the capacity loss is only 17.6 %.Meanwhile,it owned a specific capacity of 410 mAh g^-1 at 4000 mA g^-1.The composites loading smaller Fe₃O₄ nanoparticles could effectively improve the conductivity of the composites and increase the specific surface of the composite,and shorten transport path of ions and electrons,thus leading to an increased specific capacity,favorable rate performance and good cyclic stability.2.The CNT@Fe₃O₄@C nanocomposites were synthesized by the microwave assisted method with subsequent heat treatment.Among them,ferric nitrate was acted as an iron source,sulfonated polymer nanotubes as carbon source and template,and dopamine hydrochloride as the adhesive.The CNT@Fe₃O₄@C nanocomposites addressed the problems of CNT@Fe₃O₄ nanocomposites,including easily fall off Fe₃O₄ nanoparticles and cyclic instability of the composites.Meanwhile,the results showed the products obtained at 180 oC and 60 min had a good electrochemical performance,which delivered a specific capacity of 767.9 mAh g^-1 at a current density of 500 mA g^-1 after 200 cycles and a specific capacity of 420 mAh g^-1 at 4000 mA g^-1.Such a unique C-Fe-C structure improved the conductivity of the composites,shortened the transportation path of ions and electrons,enlarged the specific surface area of the materials and enhanced the structural stability of the composites,which greatly helped an excellent reversible capacity,favorable rate capability and good cyclic stability of the composites.3.Porous sandwich-like CNT@Fe₃O₄@C coaxial nanocables have been cleverly constructed by a low-temperature reflux process.During the process of preparation,ferric nitrate was acted as an iron source,sulfonated polymer nanotubes as carbon source and template,and glucosum anhydricum as the coating agent.Porous sandwich-like CNT@Fe₃O₄@C coaxial nanocables solved the problems of an undesired coating effect and fewer loaded Fe₃O₄ nanoparticles of CNT@Fe₃O₄@C nanocomposites.Meanwhile,the results displayed that the electrochemical performance of the composites were better under the acid environment,which delivered a favorable specific capacity of 724.8 mA h g^-1 at 1000 mA g^-1,and exhibited a specific capacity of 700 mAh g^-1 at 4000 mA g^-1.The improved electrochemical performance of sandwich-like CNT@Fe₃O₄@C coaxial nanocables are attributed to the special sandwich-like structural features,shortened diff usion distance of ions and electrons,hierarchical porosity,enlarged electrode/electrolyte interfacial surface area and enhanced mechanical stability.