Electrochemical performance of anodized TiO 2 Nanotubes for rechargeable Lithium Batteries
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Electrochemical performance of anodized TiO2 Nanotubes for rechargeable Lithium Batteries R. Prasada Rao*,1, L. Kangle1, S. Adams1, M.V. Reddy2 and B.V.R. Chowdari 2 1 Department of Materials Science and Engineering, National University of Singapore, Singapore, 117574, Singapore 2 Department of Physics, National University of Singapore, Singapore, 119260, Singapore Email: *[email protected]
ABSTRACT The electrochemical storage performance of anatase TiO2 nanotubes (NT) is compared to the performance of TiO2 nanotubes covered by sulfur. Charge/discharge curves and cycling performance of TiO2 NT with and without sulfur deposition with respect to lithium anodes are demonstrated in electrochemical test cells. At 0.5C cycle rate the TiO2 NT exhibited a first cycle specific charge/discharge capacity of 180/155 mAh/g, whereas the TiO2 NT deposited with sulfur showed a remarkably higher performance at 0.5C cycle rate with first cycle charge/ discharge specific capacities of 258/260 mAh/g and a coulombic efficiency of 98%. INTRODUCTION Electrochemical energy storage devices with high energy and power density are critical power sources in powering electric vehicles and portable electronic devices because of their high capability. Among the commercial batteries in the market (lead acid, nickel metal hydride and nickel cadmium batteries), lithium-ion batteries exhibit crucial advantages in terms of high energy storage capacity, reduced size and weight and low toxicity. However, work is still to be done to improve their benefits and the performances of the electrodes and the electrolyte [1–4]. Nowadays, the improvement of carbon-based anodes and intercalation cathode materials such as LiCoO2, or their replacement by novel high performance electrode materials are subjects of intense study. The key resides in the use of nano structured materials that can improve the kinetic properties for lithium insertion and extraction [3]. Anatase TiO2 is a potential alternative for the graphite anode with improved safety. Its higher voltage operation (ca. 1.75V vs. Li+/Li) eliminates the risk of shortcircuits by Li dendrite growth on overcharging. Moreover, the deposition of metallic Li also causes irreversible capacity losses as a consequence of electrolyte decomposition and the formation of a passive Solid Electrolyte Interface layer (SEI). The absence of such a SEI in cells with TiO2 anodes improves the overall electrode kinetics. While the higher operation voltage of TiO2 anodes also reduces the energy density (e.g. in batteries with LiFePO4 cathodes), this effect could be mitigated when higher voltage cathode materials such as spinel-type LiMn2O4, LiVPO4 are used [5–6]. With the recently emerging 5V cathode materials, such as LiM0.5Mn1.5O4 (M= Ni, Co) and LiCoPO4 [7,8], the operating voltage of batteries using higher voltage anode material, such as TiO2 and/or Li4Ti5O12 [9,10] could be comparable with current Lithium ion batteries. Safer high performance cells built according to this concept belong to the category of third generation Li-
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