Electrospinning-derived hybrid nanofibers with tailored morphologies : mechanism and electrochemical properties
Date of Issue2012
School of Materials Science and Engineering
Carbon-based hybrid nanofibers, which are composites derived from incorporation of organic or inorganic nanofillers into one-dimensional carbon matrix, have attracted tremendous attention for applications in lithium ion batteries (LIBs) due to their large aspect ratio, high specific surface area and fast lithium ion intercalation/de-intercalation rate. The organic or inorganic materials could be embedded in or wrapped over the amorphous or graphitized carbon phase, depending on the preparation method. Electrospinning followed by carbonization is one of the most powerful techniques to prepare CNFs since it allows mass production, morphology and structure control, and extremely large aspect ratio. Inorganic components have been combined with electrospinning-derived CNFs to further improve the electrochemical performance, for which the morphologies and structures of the hybrid nanofibers are critical for the improvement. Although different morphologies have been formed via electrospinning, leading to varied performance, the tailoring of morphologies of carbon-based hybrid nanofibers through carbonization is not yet well understood. Thus in this work, a systematic study was conducted on the effect of carbonization on morphologies and structures of carbon-based hybrid nanofibers. Their electrochemical properties were studied as anode of LIBs and correlated to the morphologies. First of all, randomly orientated carbon-SnO2 hybrid nanofibrous mats were prepared via conventional single-spinneret electrospinning followed by carbonization. Various tin-containing salts, including tin acetate (Sn(CH3COO)2), tin chloride dihydrate (SnCl2·2H2O), tin sulphate (SnSO4), tin sulphide (SnS), were used as precursors of SnO2, and polyacrylonitrile (PAN) was used as carbon source. The morphologies and structures of the hybrid nanofibers were investigated. It is shown that under the same carbonization conditions, carbon-SnO2 hybrid nanofibers with different morphologies are formed from different SnO2 precursors. The SnO2 nanoparticles are uniformly distributed in CNFs in SnSO4 and SnS-derived hybrid CNFs, while a carbon-SnO2 core-shell morphology is achieved in Sn(CH3COO)2 and SnCl2·2H2O-derived ones. Corresponding SnO2 nanofibers with varied structures, in either solid or hollow, are also produced through simply burning out the carbon phase. When the carbon phase is completely removed, the nanoparticles touch each other, forming 1D aggregates. Thus, the hollow SnO2 nanofibers actually consist of small SnO2 nanoparticles.