Contents lists available at ScienceDirect Nano Energy journal homepage: www.elsevier.com/locate/nanoen Full paper Mesoporous single-crystal-like TiO 2 mesocages threaded with carbon nanotubes for high-performance electrochemical energy storage Yiting Peng a,1 , Zaiyuan Le b,1 , Meicheng Wen c , Dieqing Zhang c , Zheng Chen b , Hao Bin Wu b , Hexing Li a,c, ⁎ , Yunfeng Lu b, ⁎ a Shanghai Key Laboratory of Materials Protection and Advanced Materials in Electric Power, College of Environmental and Chemical Engineering, Shanghai University of Electric Power, Shanghai 200090, PR China b Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, CA 90095, United States c Education Ministry Key Lab of Resource Chemistry and Shanghai Key Laboratory of Rare Earth Functional Materials, Department of Chemistry, Shanghai Normal University, Shanghai 200234, PR China ARTICLE INFO Keywords: Nanocomposite TiO 2 Single-crystalline Carbon nanotubes Energy storage ABSTRACT A novel nanocomposite based on mesoporous single-crystalline TiO 2 particles (TiO 2 mesocages) threaded with carbon nanotubes (CNTs) has been successfully synthesized via a facile solvothermal method. The unique hybrid architecture endows the nanocomposite with facile ion and electron transport pathways, abundant active surface sites and high structure robustness. As a result, remarkable electrochemical lithium storage properties in terms of high capacity, excellent rate capability and ultra-stable long-term cycling performance have been achieved by the CNTs-threaded TiO 2 mesocages. 1. Introduction Titanium dioxide (TiO 2 ) has been considered as a promising electrode material for lithium-ion storage due to its excellent charge storage capability, low cost and environmental benignity [1–5]. However, its poor ionic (10 -11 –10 -17 cm 2 s -1 ) and electronic (10 -8 – 10 -11 S cm -1 ) conductivity and relatively low lithium-storage capacity (150–200 mAh g -1 ) pose fundamental challenges towards high-perfor- mance devices [6–8]. To date, extensive efforts have been devoted to the control of polymorph and micro-/nanostructure [3,6,7,9,10]. Titanium dioxides with anatase [11], rutile [12] and TiO 2 -B (bronze) [11] phases have been systematically investigated. Although TiO 2 -B usually shows higher capacity and faster lithiation/delithiation kinetics than anatase and rutile, its synthesis often requires complicated and harsh conditions, which makes it less attractive for large-scale applica- tions. On the other hand, various composite architectures have been developed based on low-dimensional TiO 2 and conductive components (e.g., RuO 2 nanocrystals, carbon black, carbon nanotubes (CNTs) and graphene), such as TiO 2 -RuO 2 nanocrystals, carbon-coated TiO 2 na- noparticles, cable-like TiO 2 -CNT composites, sandwich-like TiO 2 -gra- phene composites, and spherical assemblies of TiO 2 nanocrystals and CNTs [13–19]. These low-dimensional TiO 2 provides shortened ion- diffusion length while the conductive constituents enable effective electron transport, affording these composites better electrochemical storage performance. Nevertheless, these TiO 2 nanocrystals are gen- erally assembled around the conductive moieties, which may easily disassemble from the conductive networks and result in rapid capacity fading. Herein, we report a novel nanocomposite architecture synthesized by in-situ growth of mesoporous single-crystal-like TiO 2 particles (mesocages) threaded through by CNTs. The synthesis procedures are illustrated in Scheme 1. Firstly, weakly-functionalized CNTs are dispersed in tert-butyl alcohol, followed by the addition of TiOSO 4 as the precursor of TiO 2 . During the subsequent solvothermal reaction, TiO 2 nanocrystals as building blocks are generated and attached onto the CNTs (step 1). Continuous attached growth of the nanocrystals eventually leading to the formation of mesoporous single-crystal-like TiO 2 particles threaded by the CNTs (step 2 & 3). Such unique architecture meets critical requirements for high-performance electro- des. 1) The highly mesoporous structure throughout the whole TiO 2 mesocages enable effective penetration of electrolyte into the relatively large crystals, offering shortened ion-diffusion length together with the small primary building nanocrystals. 2) The in-situ growth method enables the intimate contacts between the TiO 2 particles and the CNTs since the conductive pathway is confined inside the large TiO 2 mesocages, which ensures excellent electronic conductivity. 3) The http://dx.doi.org/10.1016/j.nanoen.2017.03.003 Received 1 February 2017; Received in revised form 2 March 2017; Accepted 2 March 2017 ⁎ Corresponding authors. 1 These authors contributed equally. E-mail addresses: hexing-li@shnu.edu.cn (H. Li), luucla@ucla.edu (Y. Lu). Nano Energy 35 (2017) 44–51 Available online 03 March 2017 2211-2855/ © 2017 Published by Elsevier Ltd. MARK