Oriented single-crystalline TiO 2 nanowires on titanium foil for lithium ion batteries
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Da Deng and Jim Yang Lee Department of Chemical and Biomolecular Engineering, Faculty of Engineering, National University of Singapore, Singapore 119260
Eray S. Aydila) Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (Received 15 January 2010; accepted 19 April 2010)
A simple and environmentally benign three-step hydrothermal method was developed for growing oriented single-crystalline TiO2-B and/or anatase TiO2 nanowire arrays on titanium foil over large areas. These nanowire arrays are suitable for use as the anode in lithium ion batteries; they exhibit specific capacities ranging from 200–250 mAh/g at charge-discharge rates of 0.3 C where 1 C is based on the theoretical capacity of 168 mAh/g. Batteries retain this capacity over as many as 200 charge-discharge cycles. Even at high charge-discharge rates of 0.9 C and 1.8 C, the specific capacities were 150 mAh/g and 120 mAh/g, respectively. These promising properties are attributed to both the nanometer size of the nanowires and their oriented alignment. The comparable electrochemical performance to existing technology, improved safety, and the ability to roll titanium foils into compact three-dimensional structures without additional substrates, binders, or additives suggest that these TiO2 nanowires on titanium foil are promising anode materials for large-scale energy storage.
I. INTRODUCTION
Rechargeable lithium ion batteries (LIBs) are important for powering mobile or portable electronic devices and for storing energy in intermittent renewable power production systems that rely on the wind and the sun. During charging and discharging, lithium ions insert into the anode and the cathode, respectively. The ideal material for the electrodes must have large surface-to-volume ratios and must be able to accept and reject a large number of lithium ions without significant degradation after many charge-discharge cycles. Nanostructured electrodes provide high electrode-electrolyte interfacial area, fast lithium ion diffusion, and can accommodate large strains. Specifically, one-dimensional (1D) nanostructures such as nanorods, nanowires, and nanotubes are emerging as a new class of electrode materials for LIBs because they can provide short ion diffusion lengths, improved electron transport, and high surface-to-volume ratios.1–26 The use of aligned 1D nanostructured materials on a conducting flexible substrate (e.g., copper or a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0204
1588
http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 8, Aug 2010 Downloaded: 13 Jan 2015
titanium foil) as the electrode could have additional benefits.1–4,19–22 Firstly, easy electrolyte diffusion into the electrode through the open space in 1D nanostructured arrays could reduce the internal resistance for thick highcapacity electrodes and thus improve power performance. Secondly, aligned 1D nanostructures could provide direct electrical pathways for enhanced charge tran
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