Silicon nanoparticles (Si NPs) wrapped by graphene in carbon nanofibers were obtained via electrospinning and subsequent thermal treatment. In this study, water-soluble poly(vinyl alcohol) (PVA) with low carbon yield is selected to make the process water-based and to achieve a high silicon yield in the composite. It was also found that increasing the amount of graphene helps keep the PVA fiber morphology after carbonization, while forming a graphene network. The fiber SEM and HRTEM images reveal that micrometer graphene is heavily folded into sub-micron scale fibers during electrospinning, while Si NPs are incorporated into the folds with nanospace in between. When applied to lithium-ion battery anodes, the Si/graphene/carbon nanofiber composites show a high reversible capacity of ∼2300 mAh g(-1) at a charging rate of 100 mA/g and a stable capacity of 1191 mAh g(-1) at 1 A/g after more than 200 cycles. The interconnected graphene network not only ensures the excellent conductivity but also serves as a buffering matrix for the mechanic stress caused by volume change; the nanospace between Si NPs and folded graphene provides the space needed for volume expansion.

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Employing circumferentially uniform air flow through the sheath layer of the concentric coaxial nozzle, the gas-assisted electrospinning (GAES) utilizes both high electric field and controlled air flow to produce nanofibers. The ability to tailor the distribution of various nanofillers (1.85-12.92 vol% of spherical SiO and Si nanoparticles) in a polyvinyl alcohol jet is demonstrated by varying airflow rates in GAES. The distribution of nanofillers is measured from transmission electron microscopy and is analyzed using an image processing technique to perform the dispersion area analysis and obtain the most probable separation between nanoparticles using fast Fourier transform (FFT). The analysis in this study indicates an additional 350% improvement in dispersion area with the application of high but controlled airflow, and a 75 percent decrease in separation between nanoparticles from the FFT. The experiments in this study are in good agreement with a coarse-grained MD simulation prediction for a polymer nanocomposite system subjected to extensional deformation. Lastly, utilizing the sheath layer air flow in production of Li-battery anode material, a 680 mAh g improvement is observed in capacity for nanofibers spun via GAES compared to ES at the same Si NP loading, which is associated with better dispersion of the electrochemically active nanoparticles.

Batteries for high-rate applications such as electric vehicles need to be efficient at mobilizing charges (both electrons and ions). To this end, choice of the conductive carbon in the electrode can make a significant difference in the performance of the electrode. In this work, graphene nanoribbons (GNRs) are explored as conductive pathways for a silicon-based anode. Water-based electrospinning is employed to directly deposit poly(vinyl alcohol) (PVA)−silicon−graphene nanoribbon composite fibers on a copper current collector. The size of the employed GNRs dictates their placement: either inside each fiber (small GNRs) or as a bridge between multiple fibers (large GNRs). Galvanostatic charge/discharge cycles reveal that fibers with GNRs have higher capacity and overall retention compared to those with corresponding precursor carbon nanotubes (CNTs). To further distinguish the effectiveness of GNRs as the conductive agent, samples with two GNRs and their parent CNTs were subject to rate-capability tests. Fibers with large GNR inclusions exhibit an excellent performance at fast rates (1400 mAh g −1 at 12.6 A g −1 ). For both pairs, enhancement in the performance of GNRs over CNTs grows with increasing rates. Finally, a small amount of large GNRs (1 wt %) is blended with small GNRs in the fibers to create synergy between intra-and interconductivity provided by small and large GNRs, respectively. The resulting fiber mat exhibits the same capacity as that of only small GNRs, even at a current rate that is 4 times higher (300 mAh g −1 at 21 A g −1 ).

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