Three-dimensional thin film for lithium-ion batteries and supercapacitors

Three-dimensional heterogeneously nanostructured thin-film electrodes were fabricated by using Ta₂O₅ nanotubes as a framework to support carbon-onion-coated Fe₂O₃ nanoparticles along the surface of the nanotubes. Carbon onion layers function as microelectrodes to separate the two different metal oxides and form a nanoscale 3-D sandwich structure. In this way, space-charge layers were formed at the phase boundaries, and it provides additional energy storage by charge separation. These 3-D nanostructured thin films deliver both excellent Li-ion battery properties (stabilized at 800 mAh cm^-3) and supercapacitor (up to 18.2 mF cm^-2) performance owing to the synergistic effects of the heterogeneous structure. Thus, Li-ion batteries and supercapacitors are successfully assembled into the same electrode, which is promising for next generation hybrid energy storage and delivery devices.