Study On Preparation And Properties Of Carbon Nanofiber/Fe₃O₄ Porous Composites For Microwave Absorption And Lithium-Ion Battery

Three-dimensional?3D? porous carbon-based materials have attracted much attention in the fields of microwave absorption materials and lithium-ion battery electron materials due to their low density and high specific surface area. However, the traditional methods for preparation of 3D porous carbon-based materials usually have some disadvantages such as complex process, high cost, and low productivity. Thus, finding an alternative method to fabricate a new 3D porous carbon-based materials is of particular importance.In this work, a new 3D porous carbon nanofiber?PBC? was fabricated through a facile pyrolysis of bacterial cellulose?BC? and then PBC was surface oxidized by nitric acid. Scanning electron microscope?SEM? and Fourier Transform infrared spectroscopy?FT-IR? results indicated that large amounts of carboxyl groups were introduced on the surface of oxidized PBC fibers. PBC/Fe₃O₄ magnetic composites were synthesized by chemical co-precipitation. SEM and transmission electron microscope?TEM? images indicated that PBC/Fe₃O₄ composites maintained the 3D porous structure of PBC. The Fe₃O₄ nanoparticles with an average of 9.3 nm in non-oxidized PBC tended to self-aggregation. However, the Fe₃O₄ nanoparticles with an average of 5.4 nm were uniformly dispersed on the surface of oxidized PBC fibers, and the content of Fe₃O₄ was increased with the improvement of concentration of iron ion. XRD and vibrating sample magnetometer?VSM? results indicated that the crystallinity and magnetization of Fe₃O₄ nanoparticles in non-oxidized PBC were higher than those of Fe₃O₄ nanoparticles in oxidized PBC. Compared with non-oxidized PBC/Fe₃O₄ composite, the impedance matching of oxidized PBC/Fe₃O₄ composites was improved. In addition, the oxidized PBC/Fe₃O₄ composites exhibited extraordinary microwave absorption properties with a minimum reflection loss of-62.1 dB at 9.12 GHz with a thickness of 3.4 mm which was much better than that of PBC, Fe₃O₄, PBC/Fe₃O₄ composite prepared by mechanical mixing, non-oxidized PBC/Fe₃O₄ composite, and other relevant carbon-based microwave absorption materials.The PBC/Fe₃O₄ composites as new lithium-ion battery anode materials were synthesized by a facile two-step method including the hydrothermal synthesis of BC/?-Fe₂O₃ precursor with a biological template of BC and the pyrolysis of BC/?-Fe2O3. SEM and TEM images and XRD results indicated that the PBC/Fe₃O₄ anodes had a 3D porous structure with excellent flexibility and structural stability. The structure of PBC/Fe₃O₄ fibers was directly related to the concentration of Fe?NO₃?₃ and pyrolysis temperature. In addition, the average particles size and crystallinity of Fe₃O₄ nanoparticles was increased with the improvement of pyrolysis temperature. The microstructure of PBC/Fe₃O₄ anode synthesized with a Fe?NO₃?₃ concentration of 0.1 mol/L and a pyrolysis temperature of 600 oC was maintained perfectly and the Fe₃O₄ nanoparticles were uniformly anchored on the surface of PBC fibers. Compared with PBC and Fe₃O₄, the cycling and rate performance of PBC/Fe₃O₄ anodes were improved significantly. The PBC/Fe₃O₄ anode synthesized with a Fe?NO3?3 concentration of 0.1 mol/L and a pyrolysis temperature of 600 oC delivered a reversible capacity of 754 mAh/g at a current density of 100 mA/g after 200 cycles and delivered a reversible capacity of 410 mAh/g at a current density of 1 A/g, which were better than those of PBC/SnO2 and PBC/Ge anodes reported in the literature.PBC-based magnetic composites with 3D porous structure had excellent microwave absorption properties and lithium-storage performance, and had great potential in the fields of microwave absorption materials and lithium-ion battery anode materials.