Graphene Folding in Si Rich Carbon Nanofibers for Highly Stable, High Capacity Li-Ion Battery Anodes

Silicon has received tremendous attention as lithium ion battery anode due to its high theoretical capacity) and low working potential versus Li⁺/Li. The major problems associated with Si are its poor conductivity and large volume change during the lithium insertion and extraction process. Previously, we prepared Si/carbon nanofibers with improved electrochemical performance of Si via environmental-friendly and cost-effective water-based electrospinning procedure [1]. In this work, we continued our effort to further improve the system. Graphene, possessing excellent mechanical property, high conductivity, and good stability, has been widely applied in the energy storage field. Herein, graphene was introduced to the Si/C nanofibers for the first time. It was found increasing graphene amount helps keep the fibers morphology after carbonization. And the fiber cross section images reveal that micrometer graphene is heavily folded into the nanometer fibers during electrospinning, while Si NPs are incorporated into the folds with nanospace inbetween. When applied as the anode material in LIBs, the composites show a high reversible capacity of ~1600 mAh g^-1 at a charging rate of 100 mA/g and a stable capacity of 890 mAh g^-1 at 1A/g after 50 cycles with 98% capacity retention. The interconnected graphene network not only ensures excellent conductivity, but also serves as a buffering matrix for the mechanic stress caused by volume change; the nanospace between Si NPs and graphene provides the space needed for volume expansion.

1. Y.S. Kim, K.W. Kim, D. Cho, N.S. Hansen, J. Lee, and Y.L. Joo, "Silicon-Rich Carbon Hybrid Nanofibers from Water-Based Spinning: The Synergy Between Silicon and Carbon for Li-ion Battery Anode Application", ChemElectroChem 1, 220-226 (2014).