Study On Preparation And Properties Of Bacterial Cellulose Based Carbon Nanofibers For Lithium And Hydrogen Storage

Recently, the investigation of carbon nanofibers (CNFs) has attracted the attention of many researchers. CNFs have many unique properties such as low density, high modular ratio, high strength ratio, high conductivity, high specific surface area and so on. CNFs have been widely used in many fields including microwave absorbing coating, hydrogen storage and lithium ion batteries. Bacterial cellulose based carbon nanofibers (BC-based CNFs) possess similar properties with other CNFs, as well as the fine network and low cost.In this study, bacterial cellulose (BC) was used as a precursor to fabricate carbonized and graphitized CNFs. Then the carbonized and graphitized CNFs were modified and fabricated composites with CuO and magnesium alloy ,respectively. X-ray diffraction (XRD), Raman spectroscopy (Raman), scanning electron microscopy (SEM), transmission electron microscopy (TEM) , specific surface area (BET), surface resistivity and lithium- ion batteries charge and discharge , hydrogen absorption were employed to investigate the lithium and hydrogen storage properties of CNFs.XRD and Raman results indicated that the graphitization degree of CNFs was quite low when pyrolysed at low temperature and increased after graphitization. Moreover, the graphitization degree increased with the raising of heat treatment temperature. The morphologies of CNFs were investigated by SEM and TEM. The results indicated that the nano-sized fibers held the fine network structure of bacterial cellulose after carbonization and graphitization. High resolution TEM (HRTEM) result showed that the nanofibers transformed from the amorphous structure to ordered sheet structure of polycrystalline graphite with increasing of pyrolysis temperature. At the same time, it was indicated that both of the test results of surface resistance and specific surface area of CNFs increased with the raising of heat treatment temperature. Lithium-ion batteries charge-discharge tests showed that the irreversible capacity of CNFs with high temperature graphitization decreased, and cycle stability has significantly improved than the low temperature carbonized CNFs. Meanwhile, the CuO / CNFs composite materials charge capacity increased significantly and the cycle stability has been improved to some extent. Hydrogen absorption tests suggested that CNFs have low hydrogen storage capacity, which can be improved by increasing of the heat treatment temperature. Moreover, the hydrogen storage capacity of CNFs can be increased by treatment of KOH and composing with magnesium alloy.In summary, this study provided a new approach to fabricate lithium-ion battery cathode materials and hydrogen storage materials, as well as a research foundation for preparation and application of CNFs.