Nanocups-on-microtubes: A unique host towards high-performance lithium ion batteries

In this work, unique carbonaceous nanocups, densely attached on a free-standing hollow microfibrous mat, were prepared via a mussel-inspired biomimetic polydopamine (PDA)-coating process using electrospun porous microfibers as the templates, followed by annealing. Electron microscopic studies show that the diameters and depths of the ellipsoid-shaped nanocups are in the range of a few hundred nanometers, and they have small openings of less than 100 nm, allowing the cups to act as nano-chambers to host other functional materials as well as nano-reactors for the synthesis of embedded nanostructures. To demonstrate the functions of such a unique hollow structure, the nanocups were used to host a MoS₂ precursor, and through hydrothermal treatment, MoS₂ nanosheets were effectively trapped in the nanocups. The MoS₂-in-nanocups were used as an anode in lithium ion batteries. Good cyclability and excellent rate capacity (around 520 mA h g^-1 at 2 A g^-1) were achieved owing to the efficient charge transport provided by the good contact of the MoS₂ nanosheets with the conductive nanocups and surrounding electrolyte. The nanocups could also act as buffering chambers to effectively accommodate the volume expansion of MoS ₂ during cycling.