Flexible hierarchical membranes of WS2 nanosheets grown on graphene-wrapped electrospun carbon nanofibers as advanced anodes for highly reversible lithium storage.

It is still very challenging to achieve effective combination of carbon nanofibers and graphene sheets. In this study, a novel and facile method is developed to prepare flexible graphene/carbon nanofiber (GCNF) membranes with every carbon nanofiber wrapped by conductive graphene sheets, resulting in a remarkable improvement of their electrical conductivity. This method only entails a moderate process of soaking the pre-oxidized electrospun polyacrylonitrile (oPAN) nanofiber membranes in graphene oxide (GO) aqueous dispersion, and subsequent carbonization of the GO/oPAN hybrid membranes. By using the highly conductive GCNF membrane as a template, hierarchical WS2/GCNF hybrid membranes with few-layer WS2 nanosheets uniformly grown on GCNF nanofibers were fabricated as high-performance anodes for lithium ion batteries. Benefiting from the synergistic effects of GCNF nanofibers and WS2 nanosheets, the resulting WS2/GCNF hybrid membranes possessed a porous structure, large specific surface area, high electrical conductivity and good structural integrity, which are favorable for the rapid diffusion of lithium ions, fast transfer of electrons and overall electrochemical stability. As a result, the optimized WS2/GCNF hybrid membrane exhibited a high initial charge capacity of 1128.2 mA h g-1 at a current density of 0.1 A g-1 and outstanding cycling stability with 95% capacity retention after 100 cycles.