In situ formation of hollow graphitic carbon nanospheres in electrospun amorphous carbon nanofibers for high-performance Li-based batteries.

We report on in situ formation of hollow graphitic carbon nanospheres (HGCNs) in amorphous carbon nanofibers (ACNFs) by a combination of electrospinning, calcination and acid treatment. The prepared carbon nanofibers contain many HGCNs on which defects such as discontinuous graphene sheets with a large d-spacing in their wall exist and provide extra sites for Li(+) storage and serve as buffers for withstanding large volume expansion and shrinkage during the Li insertion and extraction procedure. Furthermore, some exposed HGCNs on the surface of the ACNFs as well as hollow structures are favorable for lithium ion diffusion from different orientations and sufficient contact between active material and electrolyte. In addition, the high conductivity architectures facilitate collection and transport of electrons during the cycling process. As a result, the ACNFs/HGCNs display a high reversible specific gravimetric capacity of ∼750 mA h g(-1) and volumetric capacity of ∼1.1 A h cm(-3) with outstanding rate capability and good cycling stability, which is superior to those of carbon nanofibers (CNFs), carbon nanotubes (CNTs), porous ACNFs, graphene nanosheets (GNSs), GNSs/CNFs, hollow carbon nanospheres and graphite. The synthesis process is simple, low-cost and environmentally friendly, providing new avenues for the rational engineering of high-energy carbon-based anode materials.