High Performance of Chemically Modified TiO<sub>2</sub> Nanotubes for Lithium-ion Microbatteries Thierry Djenizian1; 1ECOLE DES MINES SAINT-ETIENNE, Gardanne, France; PAPER: 203/Battery/Regular (Oral) SCHEDULED: 16:45/Mon./Asian (60/3rd) ABSTRACT: Modern microelectronic devices such as backup power for computer memories, MicroElectroMechanical Systems (MEMS), medical implants, smart cards, Radio-Frequency Identification (RFID) tags, and remote sensors have necessitated the development of high performance power sources at the microscale. In this context, the development of three-dimensional (3D) microbatteries forms a viable alternative to provide high volumetric energy densities to meet the demands of these devices.[1] The development of nano-architectured electrodes is one of the most promising approaches to realize the 3D paradigm of microbatteries.[2] Among all the potential anode materials, TiO<sub>2</sub> nanotubes (TiO<sub>2</sub>-NTs) possess remarkable characteristics for the design of 3D Li-ion microbatteries. Self-organized nanotubular materials allow a good diffusion of Li ions in the porous structures, and the 1D morphology allows an efficient charge transfer along the axis of the tube that results in a good apparent electronic conductivity of the TiO<sub>2</sub>-NTs layer, when compared to a film composed of nanoparticles [3,4]. Anatase TiO<sub>2</sub> can accommodate only 0.5 Li<sup>+</sup> per formula unit, corresponding to a theoretical capacity of 168 mAh g<sup>-1</sup>. Hence, several approaches have been investigated to improve the overall performance of TiO<sub>2</sub>-NTs for the design of high-performance Li-ion microbatteries. Doping with aliovalent ions like Niobium (Nb<sup>5+</sup>) is also a facile strategy to modify the electronic properties of titanium oxide and thereby enhance the electrochemical performance.[5,6] <br />We report the fabrication of self-supported Nb doped TiO<sub>2</sub>-NTs by anodization of Nb/Ti alloys devoid of any carbon additives or binders. An increase in the capacity of the TiO<sub>2</sub>-NTs was observed as the Nb doping concentration increased. Such a composition of 10 wt.% Nb doped TiO<sub>2</sub>-NTs (Nb10-TiO<sub>2</sub>-NTs) showed a first cycle capacity of 200 mAh.g<sup>-1</sup> (0.144 mAh.cm<sup>-2</sup>) compared to pristine TiO<sub>2</sub>-NTs, which gave a capacity of 115 mAh.g<sup>-1</sup> (0.078 mAh.cm<sup>-2</sup>) at C/10. Galvanostatic cycling tests at various C-rates revealed the influence of Nb doping in the TiO<sub>2</sub>-NTs. Compared to pristine TiO<sub>2</sub>-NTs, the discharge capacities of doped nanotubes are improved and almost doubled when the Nb concentration reaches 10 wt.%. Besides a good cycling behaviour at multiple C-rates, an overall capacity retention of 87 % is achieved after 100 cycles. According to Electrochemical Impedance Spectroscopy measurements, the enhanced electrochemical performance of the Nb-doped TiO<sub>2</sub>-NTs is attributed to their higher electronic conductivity. References: [1] B.L. Ellis, P. Knauth, T. Djenizian, Three-Dimensional self-supported metal oxides for advanced energy storage, Adv. Mater. 26 (2014) 3368-3397.<br />[2] J.W. Long, B. Dunn, D.R. Rolison, H.S. White, Three-Dimensional Battery Architectures, Chem. Rev., 104 (2004), 4463-4492.<br />[3] G.F. Ortiz, I. Hanzu, T. Djenizian, P. Lavela, J.L. Tirado, P. Knauth, Alternative Li-Ion Battery Electrode Based on Self-Organized Titania Nanotubes, Chem. Mater., 21 (2009), 63-67.<br />[4] T. Djenizian, I. Hanzu, P. Knauth, Nanostructured negative electrodes based on titania for Li-ion microbatteries , J. Mater. Chem., 21 (2011), 9925-9937.<br />[5] Y.Wang, B. M Smarsly, I. Djerdj, Niobium Doped TiO2 with Mesoporosity and Its Application for Lithium Insertion, Chem. Mater., 22 (2010), 6624-6631.<br />[6] M. Fehse, S. Cavaliere, P. E. Lippens, I. Savych, A. Iadecola, L. Monconduit, D. J. Jones, J. Roziere, F. Fischer, C. Tessierand, L. Stievano, Nb-Doped TiO2 Nanofibers for Lithium Ion Batteries, J. Phys. Chem. C, 117 (2013), 13827-13835. |