Ultrathin TiO 2 (B) Nanorods with Superior Lithium-Ion Storage Performance Roberto Giannuzzi, † Michele Manca,* ,† Luisa De Marco, † Maria R. Belviso, ‡ Alessandro Cannavale, † Teresa Sibillano, § Cinzia Giannini, § P. Davide Cozzoli, ‡,∥ and Giuseppe Gigli †,‡,∥ † Center for Bio-Molecular Nanotechnology, Fondazione Istituto Italiano di Tecnologia, Via Barsanti, 73010 Arnesano, Lecce, Italy ‡ National Nanotechnology Laboratory (NNL), CNR Istituto Nanoscienze, c/o Distretto Tecnologico, Via Arnesano 16, 73100 Lecce, Italy § Istituto di Cristallografia (IC) CNR, via Amendola 122/O, 70126 Bari, Italy ∥ Dipartimento di Matematica e Fisica “E. De Giorgi”, Universita’ del Salento, Via Arnesano, 73100 Lecce, Italy * S Supporting Information ABSTRACT: The peculiar architecture of a novel class of anisotropic TiO 2 (B) nanocrystals, which were synthesized by an surfactant-assisted nonaqueous sol−gel route, was profitably exploited to fabricate highly efficient mesoporous electrodes for Li storage. These electrodes are composed of a continuous spongy network of interconnected nanoscale units with a rod-shaped profile that terminates into one or two bulgelike or branch-shaped apexes spanning areas of about 5 × 10 nm 2 . This architecture transcribes into a superior cycling performance (a charge capacitance of 222 mAh g −1 was achieved by a carbon-free TiO 2 (B)- nanorods-based electrode vs 110 mAh g −1 exhibited by a comparable TiO 2 -anatase electrode) and good chemical stability (more than 90% of the initial capacity remains after 100 charging/discharging cycles). Their outstanding lithiation/delithiation capabilities were also exploited to fabricate electrochromic devices that revealed an excellent coloration efficiency (130 cm 2 C −1 at 800 nm) upon the application of 1.5 V as well as an extremely fast electrochromic switching (coloration time ∼5 s). KEYWORDS: TiO 2 (B) nanorods, mesostructured electrodes, lithium-ion storage, electrochemical-impedance spectroscopy ■ INTRODUCTION Titanium dioxide (TiO 2 ) nanomaterials represent a class of a chemically inert, nontoxic, biocompatible, and inexpensive high-band-gap semiconductors characterized by wide range of interesting chemical-physical properties, including a high refractive index, good electric conductivity, excellent UV- absorption capability, and, in particular, a remarkable (photo)- catalytic activity. 1,2 Because of its particular electronic band structure and photochemical stability, nanoscale TiO 2 has been demonstrated to be a suitable platform for many solar-energy conversion applications ranging from dye-sensitized solar cells and water-splitting photoelectrolytic systems for hydrogen production to photocatalysts for the demolition of pollutants and conversion of CO 2 into added-valued chemicals and small hydrocarbon fuels. 1 TiO 2 has also recently attracted significant attention as an efficient lithium-ion (Li + ) anode material Received: November 7, 2013 Accepted: January 8, 2014 Published: January 8, 2014 Research Article www.acsami.org © 2014 American Chemical Society 1933 dx.doi.org/10.1021/am4049833 | ACS Appl. Mater. Interfaces 2014, 6, 1933−1943