Electrospun TiO 2 −Graphene Composite Nanofibers as a Highly Durable Insertion Anode for Lithium Ion Batteries Xiang Zhang, †,∥,# Palaniswamy Suresh Kumar, ∥,#,§ Vanchiappan Aravindan, ⊥,# Hui Hui Liu, ‡,# Jayaraman Sundaramurthy, ∥,§ Subodh G. Mhaisalkar, ⊥ Hai Minh Duong, † Seeram Ramakrishna,* ,†,§ and Srinivasan Madhavi* ,∥,⊥ † Department of Mechanical Engineering, ‡ Department of Chemistry, and § Center for Nanofibers and Nanotechnology, National University of Singapore, Singapore 117576, Singapore ∥ School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore ⊥ Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, Research Techno Plaza, 50 Nanyang Drive, Singapore 637553, Singapore * S Supporting Information ABSTRACT: We report the synthesis and electrochemical performance of one-dimensional TiO 2 −graphene composite nanofibers (TiO 2 −G nanofibers) by a simple electrospinning technique for the first time. Structural and morphological properties were characterized by various techniques, such as X- ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and BET surface area analysis. Lithium insertion properties were evaluated by both galvanostatic and potentiostatic modes in half-cell configurations. Cyclic voltammetric study reveals the Li-insertion/extraction by a two-phase reaction mechanism that is supported by galvanostatic charge−discharge profiles. Li/TiO 2 −G half-cells showed an initial discharge capacity of 260 mA h g −1 at current density of 33 mA g −1 . Further, Li/TiO 2 −G cell retained 84% of reversible capacity after 300 cycles at a current density of 150 mA g −1 , which is 25% higher than bare TiO 2 nanofibers under the same test conditions. The cell also exhibits promising high rate behavior with a discharge capacity of 71 mA h g −1 at a current density of 1.8 A g −1 . 1. INTRODUCTION Lithium ion battery (LIB) technology has been the forerunner in portable and mobile applications. Their performance, however, still lags behind for emerging applications such as electric vehicles (EV) and hybrid electric vehicles (HEV). 1−3 New LIB electrode materials that would offer not only high specific capacities but also safety and cycling durability are essential for high-volume LIB applications. 4,5 Titanium dioxide, TiO 2 (anatase), has emerged as a promising LIB anode alternative due to its high theoretical capacity (335 mA h g −1 ), flat operating potential (arising from two phase-reaction mechanism), and low volume expansion during lithium intercalation/deintercalation (3−4%) leading to long cycle life and durability. In addition, TiO 2 is an abundant, low-cost, environmentally benign electrode material that offers enhanced safety as compared to graphite, owing to its higher insertion potential (∼1.7 V vs Li) that prohibits lithium plating. 6,7 However, the practical electrochemical performance of anatase-TiO 2 is still not optimal due to poor electron transport, aggregation tendency of TiO 2 nanoparticles, slow Li ion diffusion, and inherent electronic conductivity issues. Ongoing research activities are targeted toward improving the ionic and electronic transport properties of titania. One such approach is tailoring particle size and morphology of anatase TiO 2 to enhance lithium diffusion and electronic conduction path. One- dimensional (1D) metal oxide nanostructured materials such as nanowires, nanotubes, and nanorods are particularly interesting in LIBs owing to the large surface to volume ratio, their vectorial ion and electron transport, and ability to accom- modate lithiation induced stresses. 8−11 To date, considerable efforts have been devoted to the synthesis of TiO 2 nanoma- terials with various morphologies through different routes such as sol−gel, micelle, reverse micelle, and hydrothermal/ solvothermal methods. 8,9,12 Another approach to improve the Li ion insertion properties of titania is to fabricate composite nanostructured electrodes that interconnect titania with a conducting additive nanophase (such as carbon, CNT) that provides a facile electron pathway. 13,14 Similarly, graphene-based materials have also been emerged as prospective electrodes in LIB applications because of their unique properties like high specific surface area (2630 m 2 g −1 ), high intrinsic mobility (200 000 cm 2 v −1 s −1 ), high Young’s Received: March 16, 2012 Revised: June 19, 2012 Published: June 28, 2012 Article pubs.acs.org/JPCC © 2012 American Chemical Society 14780 dx.doi.org/10.1021/jp302574g | J. Phys. Chem. C 2012, 116, 14780−14788