Letter pubs.acs.org/NanoLett
Self-Supported Li4Ti5O12−C Nanotube Arrays as High-Rate and LongLife Anode Materials for Flexible Li-Ion Batteries Jun Liu,‡ Kepeng Song,§ Peter A. van Aken,§ Joachim Maier,‡ and Yan Yu*,†,‡ †
CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China ‡ Max Planck Institute for Solid State Research, Heisenbergstr. 1, Stuttgart, 70569, Germany § Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, Stuttgart, 70569, Germany S Supporting Information *
ABSTRACT: Self-supported Li4Ti5O12−C nanotube arrays with high conductivity architectures are designed and fabricated for application in Li-ion batteries. The Li4Ti5O12 nanotube arrays grow directly on stainless steel foil by a facile templatebased solution route, further enhancing electronic conductivity by uniform carboncoating on the inner and outer surfaces of Li4Ti5O12 nanotubes. Owing to the shortened Li+ diffusion distance, high contact surface area, sufficient conductivity, and very good structure stability of the nanotube arrays, the self-supported Li4Ti5O12−C nanotube arrays exhibit remarkable rate capability (a reversible capability of 135 mA h g−1, 105 mA h g−1, and 80 mA h g−1 at 30C, 60C, and 100C, respectively) and cycling performance (approximate 7% capacity loss after 500 cycles at 10C with a capacity retention of 144 mA h g−1). KEYWORDS: Li-ion batteries, Li4Ti5O12, nanotubes, arrays, ultrafast charge/discharge
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substrates before being assembled into a battery cell. Obviously, this process not only introduces additional undesirable interfaces in the electrode but also inevitably compromises the overall specific energy storage capacity. Constructing such arrays (e.g., Co3O4 nanowire arrays21 and Si nanowires arrays22) on current collectors may overcome the above drawbacks. Furthermore, if the substrate is flexible, such arrayed electrode materials on bendable substrate could be of use in flexible electronics.23,24 Recently, self-supported Li4Ti5O12 nanowire arrays deposited on Ti foil were successfully fabricated25 and found to exhibit good rate capability (121 mA h g−1 at 30C) and good cycle life (approximate 5% capacity loss after 300 cycles at 5C). As compared to dense nanowire arrays of electrode materials, hollow-structured nanowire arrays (i.e., nanotubes arrays) are expected to offer special advantages. First, the hollow structure increases the electroactive interface for transfer of Li+ during charge/discharge.26 Second, the electronic conductivity can be significantly enhanced by both inner and outer surface-coating with conductive carbon thin layers. Inspired by these findings, herein we report a facile and scalable synthesis of well-aligned Li4Ti5O12−C nanotube arrays on stainless steel foil. It is the first time that well-aligned Li4Ti5O12−C nanotube arrays have been fabricated. When used as a binder-free anode in Li-ion
he development of high rate Li-ion batteries with improved safety and a long cycle life is essential for most battery applications, in particular for electronics and electrotraction.1−9 As far as the current Li-ion batteries using graphite anodes are concerned, the rate performance and cycle life are poor, and serious safety issues are caused by the solid electrolyte interphase film (SEI).7 As an alternative material to graphitic carbon, the Li4Ti5O12 spinel has been extensively studied as most promising anode for large-scale Li-ion batteries. Such anodes exhibit a flat and a comprehensively high potential around 1.5 V (vs Li/Li+), excellent cycle life due to negligible volume change, and high thermal stability, enabling their use at elevated temperature.10−13 Furthermore, the contact to typical electrolytes is SEI free, which allows battery electrodes to meet high power and abuse tolerance requirements needed for electric vehicles.10 However, the low electronic conductivity (
