Additive-free synthesis of unique TiO_2 mesocrystals with enhanced lithium-ion intercalation properties

摘要

Unique nanorod-like mesocrystals constructed from ultrathin rutile TiO_2 nanowires were successfully fabricated for the first time using a low-temperature additive-free synthetic route, and the mesocrystal formation requirements and mechanism in the absence of polymer additives were discussed. The ultrathin nanowires were highly crystalline and their diameters were found to be ca. 3-5 nm. The rutile TiO_2 mesocrystals were formed through homoepitaxial aggregation of the ultrathin nanowires via face-to-face oriented attachment, accompanied and promoted by simultaneous phase transformation from the precursor hydrogen titanate to rutile TiO_2. The rutile TiO_2 mesocrystals thus synthesized were subjected to detailed structural characterization by means of scanning and transmission electron microscopy (SEM/TEM) including high-resolution TEM (HRTEM) and selected area electron diffraction (SAED), X-ray diffraction (XRD) and Raman spectroscopy. The rutile TiO_2 mesocrystals were tested for lithium-ion intercalation and demonstrated large reversible charge-discharge capacity and excellent cyclic stability, which could be attributed to the intrinsic characteristics of the mesostructured TiO_2 constructed from ultrathin nanowires offering large specific surface area for intercalation reaction and easy mass and charge transport, as well as sufficient void space accommodating volume change.