Tube-in-tube composite nanofibers with high electrochemistry performance in energy storage applications

As a kind of excellent structure, nanotubes are combined with the advantages of the hollow structure and one-dimensional structure. Especially, the metal oxide nanotubes have broad application prospects in the field of energy storage and conversion. In this paper, we design a simple method to synthesize 12 kinds of carbon-coated tube-in-tube composite nanofibers (TiTCNFs) via a single-spinneret green electrospinning and subsequent pyrolysis processes, including carbon-coated metal TiTCNFs (Ni@C), carbon-coated single metal oxides TiTCNFs (Fe3O4@C, NiO@C, Co3O4@C, Mn3O4@C, CuO@C) and carbon-coated binary metal oxides TiTCNFs (CoFe2O4, CoMn2O4, MnFe2O4, NiCo2O4, NiFe2O4, NiMn2O4). The carbon-coated metal oxides TiTCNFs have superior electrochemical performances in Li-ion batteries and supercapacitors compared with hollow nanotube and pea-like structured composite nanofibers. The good electrochemical performances of TiTCNFs ascribe to the moderate carbon content, large specific surface area, and unique tube-in-tube structure effectively relieving the volume effect during the cycling process. The design and synthetic strategy is available for fabricating a wide variety of carbon-coated metal oxide nanotubes.