Nano-confinement coating strategy derived Matryoshka-like carbon nanotubes@anatase nanocrystalline@amorphous carbon nanofibers for ultrafast sodium ion storage

Titania is considered to be an attractive candidate as anode for sodium ion batteries due to excellent cycle stability, advanced safety features, and small volume deformation in the charge-discharge process. However, limited by sodium storage mechanism, the fast charge and discharge performance of multi-crystals titania is failed to satisfy the requirements of commercial application. Here, we develop a Matryoshka-like carbon nanotubes@anatase nanocrystalline@amorphous carbon (CNTs@aTiO2@C) nanofibers for ultrafast sodium ion storage. A nano-confinement coating strategy is demonstrated for constructing an intermediate layer assembled by ultrafine nanocrystalline (2-3 nm) of anatase. The synthesized Matryoshka-like nanofibers with diameters of ∼95 nm consists of amorphous carbon outer layer (10-13 nm), anatase nanocrystalline assembled intermediate layer (13-15 nm), and carbon nanotube core. Benefit from the ultra-refinement of anatase nanocrystalline and Matryoshka-like micro-morphology, the proportion of the capacitive-controlled contribution are up to 90.1 %, 90.6%, 91.9 %, 92.3%, and 93.6% with sweep rate increased from 0.2 to 0.4, 0.6, 0.8, and 1.0 mV s−1, thus result in an outstanding reversible specific capacities of ∼120 mA h g−1 with Coulombic efficiency of ∼99.5% after long-life of 10000 cycles at ultrafast rate of 10 A g−1.